Image coding method including selecting a context for performing arithmetic coding on a parameter indicating a coding-target coefficient included in a sub-block

ABSTRACT

An image coding method for coding an image on a block-by-block basis, includes: selecting, for each of a plurality of sub-blocks included in a coding-target block and each including a plurality of coefficients, a context for performing arithmetic coding on a parameter indicating a coding-target coefficient included in the sub-block from a context set corresponding to the sub-block, based on at least one reference coefficient located around the coding-target coefficient, the coding-target block being a transform unit; and performing arithmetic coding on the parameter indicating the coding-target coefficient using probability information about the selected context, wherein, in the selecting, the context is selected from the context set, the context set corresponding to a sum of (i) a value indicating a position in a horizontal direction of the sub-block in the coding-target block and (ii) a value indicating a position in a vertical direction of the sub-block in the coding-target block.

FIELD

The present disclosure relates to an image coding technique and an imagedecoding technique for performing arithmetic coding and arithmeticdecoding, respectively.

BACKGROUND

Recent years have seen a significant technical development in digitalvideo apparatuses and demands for compression-coding a video signal (aplurality of pictures arranged in time series). Such a compression-codedvideo signal is, for example, recorded on a recording medium such as aDVD and a hard disc, and is distributed on a network. The H.264/AVC(MPEG-4 AVC) is one of the image coding standards, and, as thenext-generation standard, the High Efficiency Video coding (HEVC)standard is currently being considered (Non-patent Literature 1).

The HEVC standard today involves a step of predicting an image to becoded, a step of calculating a residual between a coding-target imageand a prediction image, a step of transforming the residual image intofrequency coefficients, and a step of performing arithmetic coding onthe frequency coefficients. In the arithmetic coding step, contextadaptive arithmetic coding is performed on the components (coefficients)included in the coding-target block in the order from highest frequencycomponents to low frequency components.

CITATION LIST Non Patent Literature 1

-   Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG16 WP3    and ISO/IEC JTC1/SC29/WG11, 6th Meeting: Torino, IT, 14-22 Jul.,    2011 JCTVC-F803_d0, Title: WD4: Working Draft 4 of High-Efficiency    Video Coding    http://phenix.it-sudparis.eu/jct/doc_end_user/documents/6_Torino/wg    11/JCTVC-F803-v2.zip

SUMMARY Technical Problem

However, in the conventional context adaptive arithmetic coding, a largeamount of load is sometimes required to select contexts for codingcoding-target coefficients.

In view of this, the present disclosure provides an image coding methodwhich enables reduction in the amount of load required to selectcontexts for coding coding-target coefficients.

Solution to Problem

An image coding method according to an aspect of the present disclosureis an image coding method for coding an image on a block-by-block basisand including: selecting, for each of a plurality of sub-blocks includedin a coding-target block and each including a plurality of coefficients,a context for performing arithmetic coding on a parameter indicating acoding-target coefficient included in the sub-block from a context setcorresponding to the sub-block, based on at least one referencecoefficient located around the coding-target coefficient, thecoding-target block being a transform unit; and performing arithmeticcoding on the parameter indicating the coding-target coefficient usingprobability information about the selected context, wherein, in theselecting, the context is selected from the context set, the context setcorresponding to a sum of (i) a value indicating a position in ahorizontal direction of the sub-block in the coding-target block and(ii) a value indicating a position in a vertical direction of thesub-block in the coding-target block.

These general and specific aspects may be implemented using a system, anapparatus, an integrated circuit, a computer program, or acomputer-readable recording medium such as a CD-ROM, or any combinationof systems, methods, integrated circuits, computer programs, orcomputer-readable recording media.

Advantageous Effects

An image coding method according to an aspect of the present disclosuremakes it possible to reduce the load of selecting contexts for codingcoding-target coefficients in context adaptive arithmetic coding.

BRIEF DESCRIPTION OF DRAWINGS

These and other objects, advantages and features of the disclosure willbecome apparent from the following description thereof taken inconjunction with the accompanying drawings that illustrate a specificembodiment of the present disclosure.

FIG. 1 is a diagram for illustrating a scheme of selecting a context forarithmetic coding of significant_flag in the underlying knowledgeforming the basis of the present disclosure.

FIG. 2 is a diagram showing an order of coding the coefficients includedin a coding-target block in the underlying knowledge forming the basisof the present disclosure.

FIG. 3A is a diagram for illustrating a context set for one of thecoefficients included in a sub-block in the underlying knowledge formingthe basis of the present disclosure.

FIG. 3B is a diagram for illustrating a context set for another one ofthe coefficients included in a sub-block in the underlying knowledgeforming the basis of the present disclosure.

FIG. 4 is a block diagram showing a structure of an image codingapparatus in Embodiment 1.

FIG. 5 is a flowchart showing a processing operation performed by theimage coding apparatus in Embodiment 1.

FIG. 6 is a block diagram showing an internal structure of a variablelength encoder in Embodiment 1.

FIG. 7 is a flowchart showing a processing operation performed by thevariable length encoder in Embodiment 1.

FIG. 8 is a block diagram showing an internal structure of asignificant_flag encoder in Embodiment 1.

FIG. 9 is a flowchart showing a processing operation performed by thesignificant_flag encoder in Embodiment 1.

FIG. 10A is a diagram showing an example of a result of grouping in thecase of a coding block of 16×16 pixels in Embodiment 1.

FIG. 10B is a diagram showing an example of a result of grouping in thecase of a coding block of 32×32 pixels in Embodiment 1.

FIG. 11A is a diagram for illustrating a context set for one of thecoefficients included in a coefficient block in Embodiment 1.

FIG. 11B is a diagram for illustrating a context set for another one ofthe coefficients included in the coefficient block in Embodiment 1.

FIG. 12 is a block diagram showing a structure of an image decodingapparatus in Embodiment 2.

FIG. 13 is a flowchart showing a processing operation performed by theimage decoding apparatus in Embodiment 2.

FIG. 14 is a block diagram showing an internal structure of a variablelength decoder in Embodiment 2.

FIG. 15 is a flowchart showing a processing operation performed by thevariable length decoder in Embodiment 2.

FIG. 16 is a block diagram showing an internal structure of asignificant_flag decoder in Embodiment 2.

FIG. 17 is a flowchart showing a processing operation performed by thesignificant_flag decoder in Embodiment 2.

FIG. 18 is a block diagram showing a structure of an image codingapparatus in Variation of Embodiment 1.

FIG. 19 is a flowchart showing a processing operation performed by theimage coding apparatus in Variation of Embodiment 1.

FIG. 20 is a block diagram showing a structure of an image decodingapparatus in Variation of Embodiment 2.

FIG. 21 is a flowchart showing a processing operation performed by theimage decoding apparatus in Variation of Embodiment 2.

FIG. 22 shows an overall configuration of a content providing system forimplementing content distribution services.

FIG. 23 shows an overall configuration of a digital broadcasting system.

FIG. 24 shows a block diagram illustrating an example of a configurationof a television.

FIG. 25 shows a block diagram illustrating an example of a configurationof an information reproducing/recording unit that reads and writesinformation from and on a recording medium that is an optical disk.

FIG. 26 shows an example of a configuration of a recording medium thatis an optical disk.

FIG. 27A shows an example of a cellular phone.

FIG. 27B is a block diagram showing an example of a configuration of acellular phone.

FIG. 28 illustrates a structure of multiplexed data.

FIG. 29 schematically shows how each stream is multiplexed inmultiplexed data.

FIG. 30 shows how a video stream is stored in a stream of PES packets inmore detail.

FIG. 31 shows a structure of TS packets and source packets in themultiplexed data.

FIG. 32 shows a data structure of a PMT.

FIG. 33 illustrates an internal structure of multiplexed data.

FIG. 34 shows an internal structure of stream attribute information.

FIG. 35 shows steps for identifying video data.

FIG. 36 shows an example of a configuration of an integrated circuit forimplementing the moving picture coding method and the moving picturedecoding method according to each of embodiments.

FIG. 37 shows a configuration for switching between driving frequencies.

FIG. 38 shows steps for identifying video data and switching betweendriving frequencies.

FIG. 39 shows an example of a look-up table in which video datastandards are associated with driving frequencies.

FIG. 40A is a diagram showing an example of a configuration for sharinga module of a signal processing unit.

FIG. 40B is a diagram showing another example of a configuration forsharing a module of the signal processing unit.

DESCRIPTION OF EMBODIMENTS

A context for performing arithmetic coding on each of coding-targetcoefficients is selected according to a coded coefficient around thecoding-target coefficient. The coding-target coefficient is subjected tothe arithmetic coding using a symbol occurrence probabilitycorresponding to the selected context.

In the case of a natural image, a lower frequency component has agreater coefficient value. For this reason, it is possible to bias asymbol occurrence probability by selecting a context with reference to acoded neighboring coefficient (a coefficient of a frequency componenthigher than the frequency component having the coding-targetcoefficient). For example, when the value of the coded neighboringcoefficient is large, it is highly likely that the value of thecoding-target coefficient is also large. For this reason, it is possibleto decrease the amount of bits to be generated by using a context for alarge value for use in the arithmetic coding of the coding-targetcoefficient when the value of the coded neighboring coefficient islarge.

In addition, the plurality of coefficients in the coding-target blockare divided into groups based on the frequency components thereof.Context sets exclusive for the respective groups are used. In otherwords, each of the coefficients is subjected to arithmetic coding usingthe context selected from the context set corresponding to the group towhich the coefficient belongs. In the case of a natural image, largecoefficients are present in a low frequency area, and small coefficientsare present in a high frequency area. For this reason, it is possible todecrease the amount of bits to be generated selectively using thecontext sets determined differently for the coefficients in the lowfrequency area and for the coefficients in the high frequency area.

In the HEVC standard, the coefficients are represented as a plurality ofparameters (such as significant_flag and greater1_flag). FIG. 1 is adiagram for illustrating a scheme of selecting a context for arithmeticcoding of significant_flag.

In FIG. 1, the coding-target block includes 16×16 pixels. Each of thepixels has a coefficient. A pixel located closer to the upper left has alower frequency component, and a pixel located closer to the lower righthas a higher frequency component.

In addition, each of the pixels belongs to a group A or a group B. InFIG. 1, the group A is a group to which pixels without hatching arebelong. The group B is a group to which pixels with hatching belong.

The context for performing arithmetic coding on significant_flagrepresenting the coefficient of each pixel is selected from the contestset corresponding to the group to which the pixel belongs. For example,a context for significant_flag of the pixel located at the upper leftend is selected from a context set A corresponding to the group A. Onthe other hand, for example, a context for significant_flag of the pixellocated at the lower right end is selected from a context set Bcorresponding to the group B.

At this time, the context is selected from the context set, based on thecoefficient of a reference pixel (a reference coefficient) locatedaround the coding-target pixel (coding-target coefficient). In FIG. 1,the context selected from the context set is determined using a total offive reference coefficients which are two coefficients located at theright side of the coding-target coefficient, two coefficients locatedbelow the coding-target coefficient, and one coefficient located at thelower right of the coding-target coefficient.

As shown in FIG. 1, the plurality of pixels are divided into groups.Thus, as described above, the use of the reference coefficient aroundthe coding-target coefficient makes it possible to select contextsutilizing the feature that the coefficients are biased depending onfrequency coefficients, and to thereby increase the coding efficiency.

FIG. 2 shows an order of coding the coefficients included in acoding-target block. In FIG. 2, the coding-target block of 16×16 pixelsis divided into a plurality of sub-blocks of 4×4 pixels enclosed by boldlines. The numbers shown in the respective sub-blocks represent thecoding order. In other words, the plurality of coefficients included inthe coding-target block are coded on a sub-block-by-sub-block basis inthe order shown by the broken arrows. In addition, the coefficientsincluded in each of the sub-blocks are coded in the order as shown bythe arrows provided in the thirteenth sub-block.

Each of FIG. 3A and FIG. 3B is a diagram for illustrating a context setfor different coefficients included in the sub-block located at theupper left end. The coding-target coefficient in FIG. 3A and thecoding-target coefficient in FIG. 3B are included in the sub-block, butbelong to different groups. In other words, the context for performingarithmetic coding on the coding-target coefficient in FIG. 3A and thecontext for performing arithmetic coding on the coding-targetcoefficient in FIG. 3B are selected from different context sets.

In other words, as shown in FIG. 1, when the plurality of pixels (theplurality of coefficients) are divided into groups, a switch betweencontext sets is made in a sub-block. In this case, for example, there isa need to determine one of the groups to which the coefficient belongsfor each of the coefficients in the sub-block. Thus, the load forselecting a context increases.

In view of this, an image coding method according to an aspect of thepresent disclosure is an image coding method for coding an image on ablock-by-block basis and including: selecting, for each of a pluralityof sub-blocks included in a coding-target block and each including aplurality of coefficients, a context for performing arithmetic coding ona parameter indicating a coding-target coefficient included in thesub-block from a context set corresponding to the sub-block, based on atleast one reference coefficient located around the coding-targetcoefficient, the coding-target block being a transform unit; andperforming arithmetic coding on the parameter indicating thecoding-target coefficient using probability information about theselected context, wherein, in the selecting, the context is selectedfrom the context set, the context set corresponding to a sum of (i) avalue indicating a position in a horizontal direction of the sub-blockin the coding-target block and (ii) a value indicating a position in avertical direction of the sub-block in the coding-target block.

According to this method, it is possible to select a context from thecontext set corresponding to the sub-block. Accordingly, it is possibleto prevent occurrence of a switch between context sets in the sub-block,and to thus reduce the load for selecting a context.

Furthermore, according to this method, it is possible to select acontext from the context set corresponding to the sum of the valuesindicating the horizontal direction position and the vertical directionposition of the sub-block in the coding-target block. Accordingly, it ispossible to use the context set adapted to the coefficient variationdepending on the frequency components, and to thus suppress decrease inthe coding efficiency due to the use of the context set corresponding tothe sub-block.

For example, in the selecting, when a horizontal-direction distance anda vertical-direction distance from a position of an upper leftcoefficient in the coding-target block to a position of thecoding-target coefficient are denoted as H and V, respectively, and wheneach of the sub-blocks has a size denoted as a in each of the verticaldirection and the horizontal direction, “an integer part of (H/a)+aninteger part of (V/a)” may be calculated as the sum.

According to this method, it is possible to easily calculate the sum ofthe values indicating the horizontal direction position and the verticaldirection position of the sub-block in the coding-target block.

For example, in the selecting, when the sum is smaller than or equal toa threshold value, the context is selected from a first context set; andwhen the sum is larger than the threshold value, the context may beselected from a second context set different from the first context set.

According to this method, it is possible to select a context from thefirst context set when the sum is smaller than or equal to the thresholdvalue, and to select a context from the second context set when the sumis larger than the threshold value. Accordingly, based on the result ofcomparison between the sum and the threshold value, it is possible toeasily make a switch between the context sets between sub-blocks.

For example, in the selecting, the threshold value may increase with anincrease in the size of the coding-target block.

According to this method, the threshold value increases with an increasein the size of the coding-target block. Accordingly, when the variationin the coefficients is different depending on the size of thecoding-target block, it is possible to select a context from anappropriate one of the context sets.

For example, the at least one reference coefficient may be a coefficientof a frequency component higher than a frequency component having thecoding-target coefficient.

According to this method, it is possible to use, as the referencecoefficient, the coefficient of a frequency component higher than thecoefficient having the coding-target coefficient. In the case of anatural image, it is highly likely that the low frequency componentcoefficients are larger in value than the high frequency componentcoefficients. Accordingly, it is possible to select the appropriatecontext utilizing the feature of the natural image by using, as thereference coefficient, the coefficient of the frequency component higherthan the coefficient having the coding-target coefficient.

For example, the parameter indicating the coding-target coefficient maybe a flag indicating whether the coding-target coefficient is 0 or not.

According to this method, it is possible to code the flag indicatingwhether the coding-target coefficient is 0 or not, as the parameterindicating the coding-target coefficient. This flag is a parameterhaving a high occurrence frequency, and thus places a great influence onthe coding efficiency. Furthermore, this flag is different from aparameter having a limited number of occurrence times in the sub-block,and thus there is no coefficient value variation depending on thesub-block. However, it is also possible to suppress decrease in thecoding efficiency by selecting a context from the context setcorresponding to the sub-block when coding such a flag.

For example, the at least one reference coefficient may be a pluralityof reference coefficients, and the context selected in the selecting maycorrespond to the number of reference coefficients having a non-zerovalue among the plurality of reference coefficients.

According to this method, it is possible to select a context using thenumber of the reference coefficients having non-zero values from amongthe plurality of reference coefficients. Accordingly, it is possible toselect the appropriate context based on the reference coefficients.

For example, the image coding method may further include: making aswitch between a first coding process conforming to a first standard anda second coding process conforming to a second standard; adding, to abit stream, identification information indicating one of the firststandard and the second standard which supports one of the first codingprocess and the second coding process to which the switch is made; andwhen the switch is made to the first coding process, the selecting andthe arithmetic coding are performed as the first coding process.

According to this method, it is possible to make a switch between thefirst coding process conforming to the first standard and the secondcoding process conforming to the second standard.

Furthermore, an image decoding method according to an aspect of thepresent disclosure is an image decoding method for decoding an imagecoded on a block-by-block basis and including: selecting, for each of aplurality of sub-blocks included in a decoding-target block and eachincluding a plurality of coefficients, a context for performingarithmetic decoding on a parameter indicating a decoding-targetcoefficient included in the sub-block from a context set correspondingto the sub-block, based on at least one reference coefficient locatedaround the decoding-target coefficient, the decoding-target block beinga transform unit; and performing arithmetic decoding on the parameterindicating the decoding-target coefficient using probability informationabout the selected context, wherein, in the selecting, the context isselected from the context set, the context set corresponding to a sum of(i) a value indicating a position in a horizontal direction of thesub-block in the decoding-target block and (ii) a value indicating aposition in a vertical direction of the sub-block in the decoding-targetblock.

According to this method, it is possible to select a context from thecontext set corresponding to the sub-block. Accordingly, it is possibleto prevent occurrence of a switch between context sets in the sub-block,and to thus reduce the load for selecting the context.

Furthermore, according to this method, it is possible to select acontext from the context set corresponding to the sum of the valuesindicating the horizontal direction position and the vertical directionposition of the sub-block in the decoding-target block. Accordingly, itis possible to use the context set adapted to the coefficient variationdepending on the frequency components, and to thus appropriately decodethe bitstream having a coding efficiency less reduced due to the use ofthe context set corresponding to the sub-block.

For example, in the selecting, when a horizontal-direction distance anda vertical-direction distance from a position of an upper leftcoefficient in the decoding-target block to a position of thedecoding-target coefficient are denoted as H and V, respectively, andwhen each of the sub-blocks has a size denoted as a in each of thevertical direction and the horizontal direction, “an integer part of(H/a)+an integer part of (V/a)” may be calculated as the sum.

According to this method, it is possible to easily calculate the sum ofthe values indicating the horizontal direction position and the verticaldirection position of the sub-block in the decoding-target block.

For example, in the selecting, when the sum is smaller than or equal toa threshold value, the context is selected from a first context set; andwhen the sum is larger than the threshold value, the context may beselected from a second context set different from the first context set.

According to this method, it is possible to select a context from thefirst context set when the sum is smaller than or equal to the thresholdvalue, and to select a context from the second context set when the sumis larger than the threshold value. Accordingly, based on the result ofcomparison between the sum and the threshold value, it is possible toeasily make a switch between the context sets between sub-blocks.

For example, in the selecting, the threshold value may increase with anincrease in the size of the decoding-target block.

According to this method, the threshold value increases with an increasein the size of the coding-target block. Accordingly, when the variationin the coefficients is different depending on the size of thedecoding-target block, it is possible to select a context from anappropriate one of the context sets.

For example, the at least one reference coefficient may be a coefficientof a frequency component higher than a frequency component having thedecoding-target coefficient.

According to this method, it is possible to use, as the referencecoefficient, the coefficient of a frequency component higher than thefrequency component having the decoding-target coefficient. In the caseof a natural image, it is highly likely that the low frequency componentcoefficients are larger in value than the high frequency componentcoefficients. Accordingly, it is possible to select the appropriatecontext utilizing the feature of the natural image by using, as thereference coefficient, the coefficient of the frequency component higherthan the frequency component having the decoding-target coefficient.

For example, the parameter indicating the decoding-target coefficientmay be a flag indicating whether the decoding-target coefficient is 0 ornot.

According to this method, it is possible to decode the flag indicatingwhether the decoding-target coefficient is 0 or not, as the parameterindicating the decoding-target coefficient. This flag is a parameterhaving a high occurrence frequency, and thus places a great influence onthe coding efficiency. Furthermore, this flag is different from aparameter having a limited number of occurrence times in the sub-block,and thus there is no coefficient value variation depending on thesub-block. However, it is also possible to suppress decrease in thecoding efficiency by selecting a context from the context setcorresponding to the sub-block when coding such a flag.

For example, the at least one reference coefficient may be a pluralityof reference coefficients, and the context selected in the selecting maycorrespond to the number of reference coefficients having a non-zerovalue among the plurality of reference coefficients.

According to this method, it is possible to select a context using thenumber of the reference coefficients having non-zero values from amongthe plurality of reference coefficients. Accordingly, it is possible toselect the appropriate context based on the reference coefficients.

For example, the image decoding method may further include: making aswitch between a first decoding process conforming to a first standardand a second decoding process conforming to a second standard, accordingto identification information indicating one of the first standard andthe second standard and added to a bitstream; when the switch is made tothe first decoding process, the selecting and the arithmetic decodingare performed as the first decoding process.

According to this method, it is possible to make a switch between thefirst decoding process conforming to the first standard and the seconddecoding process conforming to the second standard.

These general and specific aspects may be implemented using a system, anapparatus, an integrated circuit, a computer program, or acomputer-readable recording medium such as a CD-ROM, or any combinationof systems, methods, integrated circuits, computer programs, orcomputer-readable recording media.

Hereinafter, embodiments are described specifically with reference tothe drawings.

Each of the exemplary embodiments described below shows a general orspecific example. The numerical values, shapes, materials, structuralelements, the arrangement and connection of the structural elements,steps, the processing order of the steps etc. shown in the followingexemplary embodiments are mere examples, and therefore do not limit thescope of the Claims. Therefore, among the structural elements in thefollowing exemplary embodiments, structural elements not recited in anyone of the independent claims the define the most generic concept aredescribed as arbitrary structural elements.

Embodiment 1 Overall Structure

FIG. 4 is a block diagram showing a structure of an image codingapparatus 100 in Embodiment 1. The image coding apparatus 100 encodes animage on a block-by-block basis. The image coding apparatus 100 includesa coding block generating unit 101, a predicting unit 102, a subtractor103, a transforming unit 104, a variable length encoder 105, an inversetransforming unit 106, an adder 107, and a frame memory 108.

The coding block generating unit 101 divides an input image (an inputpicture) into a plurality of coding blocks. A coding block is, forexample, a unit (transform unit) based on which frequency transform isperformed. The transform unit has a size smaller than or equal to acoding unit. The coding block generating unit 101 sequentially outputsthe plurality of coding blocks to the predicting unit 102 and thesubtractor 103.

The predicting unit 102 generates a prediction image (prediction block)for each of the coding blocks. For example, the predicting unit 102generates a prediction block using inter prediction or intra prediction.

The subtractor 103 subtracts the prediction image for the coding blockfrom the image of the coding block to generate a prediction error image(residual block) for the coding block.

The transforming unit 104 performs frequency transform on the residualblock to generate a plurality of frequency coefficients. It is to benoted that the transforming unit 104 quantizes the plurality offrequency coefficients as necessary to generate a plurality of quantizedcoefficients. Hereinafter, the frequency coefficients and the quantizedcoefficients are simply referred to as coefficients without beingdistinguished from each other.

The variable length encoder 105 performs variable length coding on theplurality of coefficients generated by the transforming unit 104.Furthermore, the variable length encoder 105 performs variable lengthcoding on prediction information (for example, motion vectorinformation). This variable length encoder 105 is described in detaillater.

The inverse transforming unit 106 performs inverse transform on theplurality of coefficients to reconstruct a residual block.

The adder 107 adds the prediction image for the coding block and thereconstructed error image to generate a decoded image (decoded block) ofthe coding block.

The frame memory 108 stores such a decoded image.

[Operation (Whole)]

Next, a description is given of a processing operation performed by theimage coding apparatus 100 configured as described above. FIG. 5 is aflowchart showing the processing operation performed by the image codingapparatus 100 in Embodiment 1.

(Step S101)

The coding block generating unit 101 divides an input image into aplurality of coding blocks. The coding block generating unit 101sequentially outputs the plurality of coding blocks to the subtractor103 and the predicting unit 102.

Here, the coding block has a variable size. Accordingly, the codingblock generating unit 101 divides an input image into a plurality ofcoding blocks based on features of the image. The minimum size for thecoding block is, for example, 4×4 pixels in the horizontal and verticalsizes. The maximum size for the coding block is, for example, 32×32pixels in the horizontal and vertical sizes.

(Step S102)

The predicting unit 102 generates a prediction block based on the codingblock and the decoded image stored in the frame memory 108.

(Step S103)

The subtractor 103 subtracts the prediction block from the input imageto generate a residual block.

(Step S104)

The transforming unit 104 transforms the residual block into a pluralityof coefficients.

(Step S105)

The variable length encoder 105 outputs a bitstream by performingvariable length coding on the plurality of coefficients.

(Step S106)

The inverse transforming unit 106 performs inverse transform on theplurality of coefficients to reconstruct a residual block.

(Step S107)

The adder 107 adds the reconstructed residual block and the predictionblock to generate a decoded block. Furthermore, the adder 107 stores thegenerated decoded block into the frame memory 108.

(Step S108)

Step S102 to Step S107 are repeated until all the coding blocks in theinput image are coded.

[Structure of Variable Length Encoder]

FIG. 6 is a block diagram showing an internal structure of a variablelength encoder 105 in Embodiment 1. In this embodiment, the variablelength encoder 105 performs coding using at least one of the followingfive parameters: significant_flag, greater1_frag, greater2_flag,level_minus3, and sign_flag. The variable length encoder 105 includes acoefficient block generating unit 111, a significant_flag encoder 112, agreater1_flag encoder 113, a greater2_flag encoder 114, a level_minus3encoder 115, and a sign_flag encoder 116.

The coefficient block generating unit 111 divides the coding block intoa plurality of coefficient blocks. The coefficient block is an exampleof a sub-block. In this embodiment, the coefficient block generatingunit 111 divides the coding block into a plurality of coefficient blocksof 4×4 pixels. In other words, in this embodiment, each of thecoefficient blocks includes sixteen coefficients.

The significant_flag encoder 112 encodes significant_flag. Thesignificant_flag is a flag indicating whether a coefficient is “0” ornot. When the value of the significant_flag is “0”, it is shown that thecoefficient is “0”. When the value of the significant_flag is “1”, it isshown that the coefficient is not “0”. The significant_flag encoder 112is described in detail later.

The greater1_flag encoder 113 encodes greater1_flag only when thesignificant_flag indicates “1” (only when the coefficient is not “0”).The greater1_flag is a flag indicating whether or not the absolute valueof the coefficient is larger than 1 or not. When the value of thegreater1_flag is “0”, it is shown that the absolute value of thecoefficient is “1”. On the other hand, when the value of thegreater1_flag is “1”, it is shown that the absolute value of thecoefficient is “2” or more.

The greater2_flag encoder 114 encodes greater2_flag only when thegreater1_flag indicates “1” (only when the absolute value of thecoefficient is “2” or more). The greater2_flag is a flag indicatingwhether or not the absolute value of the coefficient is larger than 2 ornot. When the value of the greater2_flag is “0”, it is shown that theabsolute value of the coefficient is “2”. On the other hand, when thevalue of the greater2_flag is “1”, it is shown that the absolute valueof the coefficient is “3” or more.

The level_minus3 encoder 115 encodes level_minus3 only when thegreater2_flag indicates “1” (only when the absolute value of thecoefficient is 3 or more). The level_minus 3 indicates a value obtainedby subtracting “3” from the absolute value of the coefficient.

The sign_flag encoder 116 encodes sign_flag only when thesignificant_flag indicates “1” (only when the coefficient is not “0”).The significant_flag is a flag indicating whether the coefficient is anegative value or not. When the value of the sign_flag is “0”, it isshown that the coefficient is a positive value. When the value of thesign_flag is “1”, it is shown that the coefficient is a negative value.

[Operation (Variable Length Coding)]

Next, a description is given of a processing operation performed by thevariable length encoder 105 configured as described above. FIG. 7 is aflowchart showing the processing operation performed by the variablelength encoder 105 in Embodiment 1.

(Step S111)

The coefficient block generating unit 111 divides a coding block intocoefficient blocks of 4×4 pixels. For example, in the case of a codingblock of 32×32 pixels, the coefficient block generating unit 111 dividesthe coding block by 8 horizontally and vertically. In addition, forexample, in the case of a coding block of 4×4 pixels, the coefficientblock generating unit 111 does not divide the coding block. It is to benoted that the following Steps S112 and S116 are performed on a basis ofa coefficient block of 4×4 pixels.

(Step S112)

The significant_flag encoder 112 performs arithmetic coding onsignificant_flag, using a context.

(Step S113)

The greater1_flag encoder 113 performs arithmetic coding ongreater1_flag, using a context.

(Step S114)

The greater2_flag encoder 114 performs arithmetic coding ongreater2_flag, based on a context.

(Step S115)

The level_minus3 encoder 115 performs arithmetic coding on level_minus3.More specifically, the level1_minus3 encoder 115 performs arithmeticcoding using a fixed symbol occurrence probability (50%), without usinga context.

(Step S116)

The significant_flag encoder 116 performs arithmetic coding onsignificant_flag. More specifically, the sign_flag encoder 116 performsarithmetic coding using a fixed symbol occurrence probability (50%),without using a context, in the same manner as the level_minus3 encoder115 does.

(Step S117)

Step S112 to Step S116 are repeated until all the coefficient blocks inthe coding block are coded.

[Structure of Significant_Flag Encoder]

FIG. 8 shows an internal structure of a significant_flag encoder 112 inEmbodiment 1. The significant_flag encoder 112 includes asignificant_flag group setting unit 121, a significant_flag setting unit122, a significant_flag memory 123, a significant_flag context selectingunit 124, an arithmetic encoder 125, and a significant_flag contextmemory 126.

The significant_flag group setting unit 121 divides the plurality ofcoefficient blocks included in the coding block into groups. Morespecifically, the significant flag group setting unit 121 divides theplurality of coefficient blocks into the groups, based on the sum of thevalues indicating the horizontal direction position and the verticaldirection position of each of the coefficient blocks in the codingblock. More specifically, the significant_flag group setting unit 121divides the plurality of coefficient blocks into the groups, forexample, based on whether the sum is smaller than or equal to athreshold value (a threshold value for group determination) or the sumis larger than the threshold value.

The values indicating the horizontal direction position and verticaldirection position of the coefficient block are derived from the valuesindicating the horizontal direction positions (the horizontal positionsof the coefficients) and vertical direction positions (the verticalpositions of the coefficients) of the respective coefficients includedin the coefficient block. More specifically, for example, thesignificant_flag group setting unit 121 derives “the integer part of(the horizontal positions of the coefficients/the horizontal size of thecoefficient block)” as the value indicating the horizontal directionposition of the coefficient block. In addition, for example, thesignificant_flag group setting unit 121 derives “the integer part of(the vertical positions of the coefficients/the vertical size of thecoefficient block)” as the value indicating the vertical directionposition of the coefficient block

Here, it is possible to use, as the horizontal position and verticalposition of the coefficient included in the coefficient block, thehorizontal and vertical direction distances from the position of theupper left coefficient in the coding block and the position of thecoefficient in the coefficient block.

The significant_flag setting unit 122 reads out, for each coefficientblock, a plurality of coefficients included in the coefficient block.The significant_flag setting unit 122 sets a value to thesignificant_flag for the coefficient, based on whether or not theread-out coefficient is “0” or not. In this embodiment, thesignificant_flag setting unit 122 sets “0” to the significant_flag whenthe coefficient is “0”, and sets “1” to the significant_flag when thecoefficient is “1”.

Furthermore, the significant_flag setting unit 122 stores thesignificant_flag for each coefficient into the significant_flag memory123.

The significant_flag memory 123 stores the significant_flag for eachcoefficient.

The significant_flag context selecting unit 124 selects, for eachcoefficient block, a context for arithmetic coding of a parameterindicating a current processing-target coefficient (coding-targetcoefficient) included in the coefficient block from the context setcorresponding to the coefficient block, based on at least one referencecoefficient around the coding-target coefficient. More specifically, thesignificant_flag context selecting unit 124 selects a context from thecontext set corresponding to the sum of the values indicating thehorizontal direction position and the vertical direction position of thecoefficient block in the coding block.

The arithmetic encoder 125 obtains the probability information about theselected context from the significant_flag context memory 126. Thearithmetic encoder 125 performs arithmetic coding on the parameterindicating the processing-target coefficient using the obtained contextprobability information. In this embodiment, the parameter is thesignificant_flag.

Furthermore, the arithmetic encoder 125 updates the context probabilityinformation stored in the significant_flag context memory 126, accordingto the value of the significant_flag.

The significant_flag context memory 126 stores the probabilityinformation about each context.

[Operation (Coding of Significant_Flag)]

Next, a description is given of the significant_flag encoder 112configured as described above. FIG. 9 shows a processing operationperformed by the significant_flag encoder 112 in Embodiment 1. It is tobe noted that the order of coding the plurality of coefficients includedin the coefficient blocks is the same as in FIG. 2. In other words, thesignificant_flag is coded on a per coefficient block basis.

(Step S121)

The significant_flag group setting unit 121 calculates a groupdetermination threshold value. For example, the significant_flag groupsetting unit 121 divides the horizontal size of the coding block by, forexample, “16”. Next, the significant_flag group setting unit 121 setsthe integer part of the division result as the group determinationthreshold value.

In other words, the significant_flag group setting unit 121 calculates alarger threshold value for a larger coding block size. In this way, whenthe coefficients are biased depending on the coding block size, it ispossible to associate an appropriate context set with the coefficientblock. It is to be noted that the threshold value may be a certain valuewhich does not depend on a coding block size. In this case, thesignificant_flag group setting unit 121 may calculate the thresholdvalue without using the coding block size.

(Step S122)

The significant_flag group setting unit 121 adds the integer part of“the coefficient horizontal position/4” and the integer part of “thecoefficient vertical position/4”. Next, the significant_flag groupsetting unit 121 compares the addition result with the groupdetermination threshold value which is set in Step S121. Here, atransition to Step S123 is made when the addition result is smaller thanor equal to the group determination threshold value, and otherwise, atransition to S124 is made.

The coefficient horizontal position and the coefficient verticalposition are the horizontal and vertical direction positions of theprocessing-target coefficients in the coding block or values indicatingthe horizontal and vertical direction positions of the processing-targetcoefficients. Here, the coefficient horizontal position and thecoefficient vertical position are horizontal and vertical directiondistances (the number of pixels) from the upper left coefficient to theprocessing-target coefficient in the coding block. In short, in the caseof the upper left coefficient, the coefficient horizontal position andthe coefficient vertical position are both “0”. It is to be noted thateach of the coefficient horizontal position and the coefficient verticalposition is divided by “4” because the horizontal size and the verticalsize of the coefficient block is “4”.

(Step S123)

The significant_flag group setting unit 121 sets “A” to the group.

(Step S124)

The significant_flag group setting unit 121 sets “B” to the group.

FIG. 10A shows an example of a grouping result in the case of a codingblock of 16×16 pixels. FIG. 10B shows an example of a grouping result inthe case of a coding block of 32×32 pixels.

As shown in FIG. 10A, in the case of the coding block of 16×16 pixels,only the upper left corner coefficient block is included in the group A.As shown in FIG. 10B, in the case of the coding block of 32×32 pixels,three coefficient blocks at the upper left side is included in the groupA.

The following Steps S125 to S139 are processes performed for eachcoefficient in the coefficient block, and are repeated until all thecoefficients in the coefficient block are processed.

(Step S125)

The significant_flag setting unit 122 determines whether or not theprocessing-target coefficient is “0”. A transition to Step S126 is madewhen the processing-target coefficient is “0”, and a transition to StepS127 is made when the processing-target coefficient is not “0”.

(Step S126)

The significant_flag setting unit 122 sets “0” to the significant_flag.The significant_flag setting unit 122 outputs the significant_flaghaving a set value “0” to the arithmetic encoder 125 and thesignificant_flag memory 123.

(Step S127)

The significant_flag setting unit 122 sets “1” to the significant_flag.The significant_flag setting unit 122 outputs the significant_flaghaving a set value “1” to the arithmetic encoder 125 and thesignificant_flag memory 123.

(Step S128)

The significant_flag context selecting unit 124 sets “0” to SNUM to beused in the following processing.

It is to be noted that the following Steps from S129 to S132 areperformed for each processed coefficient, and are repeated until all theprocessed coefficients are processed.

(Step S129)

The significant_flag context selecting unit 124 determines whether ornot the processed coefficient is of a frequency component higher thanthe frequency component having processing-target coefficient. Atransition to Step S130 is made when the processed coefficient is of thefrequency component higher than the frequency component havingprocessing-target coefficient, and otherwise, a transition to Step S133is made. In other words, the significant_flag context selecting unit 124uses, as a reference coefficient, the coefficient of the frequencycomponent coefficient higher than the frequency component having theprocessing-target coefficient.

It is to be noted that the significant_flag context selecting unit 124determines whether or not the processed coefficient is of the frequencycomponent higher than the frequency component having processing-targetcoefficient, by determining the presence direction of the processedcoefficient from among the directions of right, lower, and lower rightwith respect to the processing-target coefficient.

(Step S130)

The significant_flag context setting unit 124 calculates the differencebetween the positions of the processed coefficient and theprocessing-target coefficient, and sets a horizontal position differenceto h and set a vertical position difference to v.

(Step S131)

The significant_flag context selecting unit 124 determines whether ornot the sum of the h and v set in Step S130 is smaller than or equal to“2”. Here, a transition to Step S132 is made when the sum of the h and vis smaller than or equal to “2”, and otherwise, a transition to StepS133 is made. In other words, the significant_flag context selectingunit 124 uses, as the reference coefficient, the processed coefficienthaving “2” or less as the sum of the h and v, and does not use, as thereference coefficient, any processed coefficient having “3” or more asthe sum of the h and v. In other words, the following five coefficientsin total are used as reference coefficients: the coefficients located,with respect to the processing-target coefficient, immediately right,next immediately right, immediately below, next below, and lower right.The positions of the reference coefficients are the same as thepositions of the reference coefficients shown in FIG. 1.

(Step S132)

The significant_flag context selecting unit 124 loads the value of thesignificant_flag of the processed coefficient (reference coefficient)from the significant_flag memory 123, and adds the loaded value to SNUM.

(Step S133)

The significant_flag context selecting unit 124 repeats Steps S129 toS132 until all the processed coefficients in the coding block areprocessed.

As the result of the processes from Step S129 to S132, the number ofreference coefficients having “1” as the value of the significant_flagis set as the final SNUM, from among the reference coefficients aroundthe processing-target coefficient. In short, the SNUM shows the numberof reference coefficients having a non-zero value from among theplurality of reference coefficients. Here, the SNUM takes a value in arange from 0 to 5.

(Step S134)

The significant_flag context selecting unit 124 determines whether ornot the SNUM is larger than “3”. Here, a transition to Step S135 is madewhen the SNUM is larger than “3”, and otherwise, a transition to StepS136 is made.

(Step S135)

The significant_flag context selecting unit 124 sets “4” to the SNUM. Inother words, the significant_flag context selecting unit 124 re-sets thevalue of the SNUM such that the value of the SNUM does not exceed “4”.

(Step S136)

The significant_flag context selecting unit 124 sets the SNUM as thecontext number when the coefficient block including theprocessing-target coefficient is included in the group A. On the otherhand, when the coefficient block including the processing-targetcoefficient is included in the group B, the significant_flag contextselecting unit 124 sets, as the context number, a result obtained byadding “5” to a SUM.

As a result, one of the context indices indicated by the context numbers0 to 4 is selected for the arithmetic coding of the processing-targetcoefficient in the coefficient block included in the group A, and one ofthe context indices indicated by the context numbers 5 to 9 is selectedfor the arithmetic coding of the processing-target coefficient in thecoefficient block included in the group B.

In other words, the significant_flag context selecting unit 124 selectsa context from a first context set (contexts with context numbers 0 to4) when the sum of the horizontal and vertical direction positions ofthe coefficient block is smaller than or equal to the threshold value.In addition, the significant_flag context selecting unit 124 selects acontext from a second context set (contexts with context numbers 5 to 9)when the sum of the horizontal and vertical direction positions of thecoefficient block is smaller than or equal to the threshold value. Inother words, one of the context sets to be used is selected depending onthe group to which the coefficient block belongs.

In addition, the context to be selected from the determined context setis determined depending on the SNUM (the number of referencecoefficients having a non-zero value from among the plurality ofreference coefficients). In other words, the significant_flag contextselecting unit 124 selects the context corresponding to the number ofreference coefficients having a value that is not “0” from among thereference coefficients (stated inversely, the number of referencecoefficients having a “0” value).

(Step S137)

The arithmetic encoder 125 loads context probability information fromthe significant_flag contest memory 126, according to the contextnumber.

(Step S138)

The arithmetic encoder 125 outputs a bitstream by performing arithmeticcoding on the significant_flag using the probability information.

(Step S139)

The arithmetic encoder 125 updates the context probability informationdepending on the value of the significant_flag, and stores the updatedcontext probability information into the significant_flag context memory126.

(Step S140)

Steps S125 to S139 are repeated until all the coefficients in thecoefficient block are processed.

Although a determination on the group to which the coefficient blockbelongs is made on a per coefficient block basis in FIG. 9, such adetermination may be made on a coefficient-by-coefficient basis. Inother words, a return to Step S125 is made when the determination resultin Step S140 is No, but it is possible to make a return to Step S122instead. Even in this case, it is possible to prevent occurrence of aswitch between context sets in a coefficient block. Furthermore, in thiscase, it is only necessary to load the context set corresponding to thedetermined group from the memory, and thus it is possible to reduce theload to be placed onto the memory.

Advantageous Effects

As described above, according to the image coding apparatus 100 in thisembodiment, it is possible to suppress decease in the coding efficiency,and to reduce the load for context selection. This advantageous effectis described in detail with reference to the drawings.

FIG. 11A and FIG. 11B are diagrams for illustrating context sets fordifferent coefficients included in a coefficient block in Embodiment 1.In the cases shown in FIGS. 11A and 11B, there is no switch such as theswitch between groups (context sets) in the coefficient block as shownin FIGS. 3A and 3B. Accordingly, the image coding apparatus 100 does notneed to determine, for each coefficient, one of the context sets whichincludes a context to be selected. Thus, it is possible to reduce theload for context selection.

Furthermore, the image coding apparatus 100 can select a context fromthe context set corresponding to the sum of the horizontal and verticaldirection positions of the coefficient block in the coding block.Accordingly, it is possible to use the context set adapted to thecoefficient variation depending on the frequency components, and to thussuppress decrease in the coding efficiency due to the use of the contextset corresponding to the coefficient block.

In addition, according to the image coding apparatus 100 in thisembodiment, it is possible to select a context from the context setcorresponding to the coefficient block when performing arithmetic codingon the significant flag. The significant_flag is a parameter having ahigh occurrence frequency, and thus places a great influence on thecoding efficiency. In addition, the significant_flag is a parameter forwhich no restriction in the number of occurrence times is placed in thecoefficient block, and is free from value variation depending on acoefficient block. The Inventors have found that selecting a contextfrom the context set corresponding to the coefficient block when codingthe significant_flag does not decrease the coding efficiency. In otherwords, the image coding apparatus 100 is capable of reducing the loadfor context selection and concurrently suppressing decrease in thecoding efficiency, in the arithmetic coding of the significant_flag.

Embodiment 2 Overall Structure

FIG. 12 shows a structure of an image decoding apparatus 200 inEmbodiment 2. The image decoding apparatus 200 decodes an image coded ona block-by-block basis. More specifically, the image decoding apparatus200 decodes an image coded by the image coding apparatus 100 inEmbodiment 1. The image decoding apparatus 200 includes a variablelength decoder 201, an inverse transforming unit 202, a predicting unit203, an adder 204, a decoded block combining unit 205, and a framememory 206.

The variable length decoder 201 performs variable decoding on abitstream to obtain a plurality of coefficients and predictioninformation (for example, motion vector information etc.) for each ofdecoding-target blocks.

The inverse transforming unit 202 performs inverse transform on aplurality of coefficients to generate error images (residual blocks) ofthe respective decoding-target blocks.

The predicting unit 203 generates a prediction image (a predictionblock) for each decoding-target block using the prediction informationand a decoded image (decoded picture) stored in the frame memory 206.

The adder 204 adds the error image of the decoding-target block and theprediction image to generate the decoded image (decoded block) of thedecoding-target block.

The decoded block combining unit 205 combines the plurality of decodedblocks to generate a decoded image. Furthermore, the decoded blockcombining unit 205 stores the decoded image into the frame memory 206.

The frame memory 206 stores such a decoded image.

[Operation (Whole)]

Next, a description is given of a processing operation performed by theimage decoding apparatus 200 configured as described above. FIG. 13 is aflowchart showing a processing operation performed by the image decodingapparatus 200 in Embodiment 2.

(Step S201)

The variable length decoder 201 performs variable length decoding on abitstream to obtain a plurality of coefficients and predictioninformation. Next, the variable length decoder 201 outputs the pluralityof coefficients to the inverse transforming unit 202, and outputs theprediction information to the predicting unit 203.

(Step S202)

The inverse transforming unit 202 performs inverse transform on theplurality of coefficients to generate a residual block.

(Step S203)

The predicting unit 203 generates a prediction block using a decodedimage stored in the frame memory 206 and the prediction informationdecoded by the variable length decoder 201.

(Step S204)

The adder 204 adds the prediction block and the residual block togenerate a decoded block.

(Step S205)

Steps S201 to S204 are repeated until all the blocks in the image aredecoded.

(Step S206)

The decoded block combining unit 205 combines the decoded blocks togenerate a decoded image. Furthermore, the decoded block combining unit205 stores the decoded image into the frame memory 206.

[Structure of Variable Length Decoder]

FIG. 14 shows an internal structure of a variable length decoder 201 inEmbodiment 2. In this embodiment as in Embodiment 1, each of thecoefficients is represented using at least one of the following fiveparameters: significant_flag, greater1_frag, greater2_flag,level_minus3, and sign_flag. Each of the parameters has the same meaningas in Embodiment 1, and thus the same description is not repeated.

The variable length decoder 201 includes a significant_flag decoder 211,a greater1_flag decoder 212, a greater2_flag decoder 213, a level_minus3decoder 214, a sign_flag decoder 215, a coefficient reconstructing unit216, and a coefficient block combining unit 217.

[Operation (Variable Length Decoding)]

Next, a description is given of a processing operation performed by thevariable length decoder 201 configured as described above. FIG. 15 is aflowchart showing a processing operation performed by the variablelength decoder 201 in Embodiment 2. It is to be noted that Steps S211 toS216 are performed for each of coefficient blocks included in adecoding-target block.

(Step S211)

The significant_flag decoder 211 performs, using a correspondingcontext, arithmetic decoding on the significant_flag of each coefficientincluded in the coefficient block. Next, the significant_flag decoder211 outputs the significant_flag to the greater1_flag decoder 212, thegreater2_flag decoder 213, the level_minus3 decoder 214, the sign_flagdecoder 215, and the coefficient reconstructing unit 216.

(Step S212)

The greater1_flag decoder 212 performs, using a corresponding context,arithmetic decoding on the greater1_flag of the coefficient having asignificant_flag of “1”. Next, the greater1_flag decoder 212 outputs thegreater1_flag to the greater2_flag decoder 213, the level1_minus3decoder 214, and the coefficient reconstructing unit 216.

(Step S213)

The greater2_flag decoder 213 performs, using a corresponding context,arithmetic decoding on the greater2_flag of the coefficient having asignificant_flag of “1” and a greater1_flag of “1”. Next, thegreater2_flag decoder 213 outputs the greater2_flag to the level_minus3decoder 214, and the coefficient reconstructing unit 216.

(Step S214)

The level_minus3 decoder 214 decodes the level_minus3 of the coefficienthaving a significant_flag of “1”, a greater1_flag of “1”, and agreater2_flag of “1”, using a fixed symbol occurrence probability (50%)without using any context. Next, the level_minus3 decoder 214 outputsthe level1_minus3 to the coefficient reconstructing unit 216.

(Step S215)

The sign_flag decoder 215 decodes the sign_flag of the coefficienthaving a significant_flag of “1”, using the fixed symbol occurrenceprobability (50%), without using any context. Next, the sign_flagdecoder 215 outputs the sign_flag to the coefficient reconstructing unit216.

(Step S216)

The coefficient reconstructing unit 216 reconstructs the coefficientusing the significant_flag, the greater1_flag, the greater2_flag, thelevel_minus3, and the sign_flag. Each of the parameters has the meaningas described earlier, the coefficient reconstructing unit 216reconstructs the coefficient according to the meaning.

(Step S217)

Steps S212 to S216 are repeated until all the coefficient blocks in thedecoding-target block are decoded.

(Step S218)

The coefficient block combining unit 217 combines all the coefficientblocks in the decoding-target block, and outputs the decoded block.

[Structure of Significant_Flag Decoder]

FIG. 16 shows an internal structure of a significant_flag decoder 211 inEmbodiment 2. The significant_flag decoder 211 includes asignificant_flag group setting unit 221, a significant_flag contextselecting unit 222, an arithmetic decoder 223, a significant_flagcontext memory 224, and a significant_flag memory 225.

The significant_flag group setting unit 221 divides the plurality ofcoefficient blocks included in the coding block into groups, asperformed by the significant_flag group setting unit 121 in Embodiment1.

The significant_flag context selecting unit 222 selects, for eachcoefficient block, a context for arithmetic coding on parametersindicating the processing-target coefficient (decoding-targetcoefficient) included in the coefficient block from the context setcorresponding to the coefficient block, based on at least one referencecoefficient around the coding-target coefficient. More specifically, thesignificant_flag context selecting unit 222 selects a context from thecontext set corresponding to the sum of the values indicating thehorizontal direction position and the vertical direction position of thecoefficient block in the coding block.

The arithmetic decoder 223 obtains the probability information about theselected context from the significant_flag context memory 224. Next, thearithmetic decoder 223 performs arithmetic decoding on the parameterindicating the processing-target coefficient using the probabilityinformation about the obtained context. In this embodiment, theparameter is the significant_flag.

Furthermore, the arithmetic decoder 223 stores the decodedsignificant_flag in the significant_flag memory 225. In addition, thearithmetic decoder 223 updates the probability information about thecontext stored in the significant_flag context memory 224, according tothe value of the significant_flag.

The significant_flag context memory 224 stores the probabilityinformation about each context.

The significant_flag memory 225 stores the significant_flag for eachcoefficient.

[Operation (Decoding of Significant_Flag)]

Next, a description is given of the significant_flag decoder 211configured as described above. FIG. 17 is a flowchart indicating aprocessing operation performed by the significant_flag decoder.

(Steps S221 to S224)

The significant_flag group setting unit 221 divides the coefficientblocks into groups in the same manner as in Steps S121 to S124 in FIG.9.

(Steps S225 to S233)

The significant_flag context selecting unit 222 selects a context basedon a reference coefficient located around the processing-targetcoefficient from the context set corresponding to the group to which thecoefficient block belongs, in the same manner as in Steps S128 to S136in FIG. 9.

More specifically, the significant_flag context selecting unit 222selects a context from a first context set (contexts with contextnumbers 0 to 4) when the sum of the horizontal and vertical directionpositions of the coefficient block is smaller than or equal to thethreshold value. In addition, the significant_flag context selectingunit 222 selects a context from a second context set (contexts withcontext numbers 5 to 9) when the sum of the horizontal and verticaldirection positions of the coefficient block is smaller than or equal tothe threshold value. In other words, the significant_flag contextselecting unit 222 selects the context corresponding to the number ofreference coefficients having a value that is not “0” from among thereference coefficients of the frequency components higher than thefrequency component having the processing-target coefficient (statedinversely, the number of reference coefficients having a “0” value).

(Step S234)

The arithmetic decoder 223 loads context probability information fromthe significant_flag context memory 224 according to the context number.

(Step S235)

The arithmetic decoder 223 performs arithmetic decoding on thesignificant_flag using the probability information.

(Step S236)

The arithmetic decoder 223 updates the context probability informationdepending on the value of the significant_flag, and stores the updatedcontext probability information into the significant_flag context memory224.

(Step S237)

Steps S225 to S236 are repeated until all the coefficients in thecoefficient block are processed.

Although a determination on the group to which the coefficient blockbelongs is made on a per coefficient block basis in FIG. 17, such adetermination may be made on coefficient-by-coefficient basis. In otherwords, a return to Step S225 is made when the determination result inStep S237 is No, but it is possible to make a return to Step S222instead. Even in this case, it is possible to prevent occurrence of aswitch between context sets in a coefficient block. Furthermore, in thiscase, it is only necessary to load the context set corresponding to thedetermined group from the memory, and thus it is possible to reduce theload placed onto the memory.

Advantageous Effects

Similarly in the case of the image coding apparatus 100 in Embodiment 1,according to the image decoding apparatus 200 in this embodiment, it ispossible to suppress decease in the coding efficiency, and to reduce theload for context selection as described above.

Although only some exemplary embodiments have been described above, thescope of the Claims of the present application is not limited to theseembodiments. Those skilled in the art will readily appreciate thatvarious modifications may be made in these exemplary embodiments andthat other embodiments may be obtained by arbitrarily combining thestructural elements of the embodiments without materially departing fromthe novel teachings and advantages of the subject matter recited in theappended Claims. Accordingly, all such modifications and otherembodiments are included in the present disclosure.

For example, in each of the embodiments, the values indicating thehorizontal direction position and the vertical direction position of thesub-block are calculated using “the integer part of (a coefficienthorizontal position/a coefficient block horizontal size)” and “theinteger part of (a coefficient vertical position/a coefficient blockvertical size)”. However, the values may be calculated using anotherscheme. For example, the values indicating the horizontal directionposition and the vertical direction position of the sub-block may becalculated using a shift operation instead of the division.

In addition, in each of the embodiments, the plurality of coefficientsincluded in the coding-target block or the decoding-target block may beclassified into two groups. However, the plurality of coefficients maybe classified into three or more groups. In this case, the groupdetermination threshold may be increased according to the number ofgroups.

In addition, the number and positions of the reference coefficients ineach of the embodiments may be exemplary, and other referencecoefficients may be used.

In addition, in each of the embodiments, each context is selected basedon the sub-block and the number of reference coefficients. However, acontext may be selected based on other conditions. For example, as acontext for performing arithmetic coding on the upper left endcoefficient (a direct component) in either a coding-target block or adecoding-target block, a context different from the context for theother coefficients may be selected.

In addition, in each of the embodiments, arithmetic coding or arithmeticdecoding is performed on the coefficients of the coding-target block orthe decoding-target block in order starting with the coefficient at theright bottom end (the highest frequency component) therein. However, itis also good to perform arithmetic coding or arithmetic decoding on thecoefficients starting with the non-zero coefficient that appears firstduring the scanning of the coefficients started with the highestfrequency component. In this case, the zero coefficients before thenon-zero coefficient that appears first during the scanning of thecoefficients started with the highest frequency component do notnecessarily need to be subjected to arithmetic coding.

In addition, in each of the embodiments, the coefficients are codedusing the five parameters. However, the coefficients may be coded usinganother combination of parameters. For example, the coefficients may becoded using the following three parameters: significant_flag,level_minus1, and sign_flag.

In addition, in each of the embodiments, the methods of selecting acontext for performing arithmetic coding and arithmetic decoding ofsignificant_flag are described. As for the other parameters, it is goodto select a context using selection methods similar to the methods usedfor the significant_flag.

In addition, in each of the embodiments, the coefficients locatedoutside the coding-target block or the decoding-target block do notalways need to be used as the reference coefficient. Furthermore, it ispossible to use, as reference coefficients, the coefficients included ina picture temporally different from the picture including thecoding-target block or the decoding-target block.

In addition, the size of the coding block (the coding-target block orthe decoding-target block) in each of the embodiments and the size ofthe coefficient block (sub-block) are exemplary, and thus other sizesare possible.

It is to be noted that the image coding apparatus 100 in Embodiment 1does not need to include all the structural elements shown in FIG. 4.For example, the image coding apparatus may be configured as describedbelow.

FIG. 18 shows a structure of an image coding apparatus 300 in Variationof Embodiment 1. The image coding apparatus 300 encodes an image on ablock-by-block basis. As shown in FIG. 18, the image coding apparatus300 includes a context selecting unit 301 and an arithmetic encoder 302.

Here, a description is given of a processing operation performed by theimage coding apparatus 300 configured as described above. FIG. 19 is aflowchart showing a processing operation performed by the image codingapparatus 300 in Variation of Embodiment 1.

(Step S301)

The context selecting unit 301 selects a context for performingarithmetic coding on the parameters indicating the coefficients includedin the coding-target block which is a transform unit. More specifically,the context selecting unit 301 selects, for each of the plurality ofsub-blocks included in the coding-target block, a context for performingarithmetic coding on the parameters indicating the coding-targetcoefficients included in the sub-block from the context setcorresponding to the sub-block, based on at least one referencecoefficient located around the coding-target coefficient.

More specifically, the context selecting unit 301 selects, for each ofthe plurality of sub-blocks, a context for performing arithmetic codingon the parameters indicating the coding-target coefficients included inthe sub-block, from the context set corresponding to the sum of thevalues indicating the horizontal direction position and the verticaldirection position of the sub-block in the coding-target block.

The sub-block is a block that is obtained by dividing the coding-targetblock. Each of the sub-blocks includes a plurality of pixels (forexample, 4×4 pixels) each including a coefficient.

Coefficients located around the coding-target coefficient means thecoefficients of the pixels located within a predetermined range withrespect to the pixel having the coding-target coefficient. For example,the coefficients located around the coding-target coefficient are thecoefficients of frequency components higher than the frequency componenthaving the coding-target coefficient.

The parameter indicating the coding-target coefficient is, for example,a flag (significant_flag) indicating whether or not the coding-targetcoefficient is 0. It is to be noted that the parameter indicating thecoding-target coefficient does not need to be significant_flag, and maybe another parameter.

(Step S302)

The arithmetic encoder 302 performs arithmetic coding on the parameterindicating the coding-target coefficient using probability informationabout the context selected by the context selecting unit 301.

As described above, the image coding apparatus 300 configured as shownin FIG. 18 can also select a context from the context set correspondingto the sum of the values indicating the horizontal direction positionand the vertical direction position of the sub-block in thecoding-target block. Accordingly, the image coding apparatus 300 cansuppress decrease in the coding efficiency and reduce the load forcontext selection.

It is to be noted that the image decoding apparatus 200 in Embodiment 2does not need to include all the structural elements shown in FIG. 12.For example, the image decoding apparatus may be configured as describedbelow.

FIG. 20 shows a structure of the image decoding apparatus 400 inVariation of Embodiment 2. The image decoding apparatus 400 decodes animage coded on a block-by-block basis.

As shown in FIG. 20, the image decoding apparatus 400 includes a contextselecting unit 401 and an arithmetic decoder 402.

Here, a description is given of a processing operation performed by theimage decoding apparatus 400 configured as described above. FIG. 21 is aflowchart showing a processing operation performed by the image decodingapparatus 400 in Variation of Embodiment 2.

(Step S401)

The context selecting unit 401 selects a context for performingarithmetic decoding on the parameters indicating the coefficientsincluded in the decoding-target block which is a transform unit. Thedetails of this processing are the same as in Step S301 in FIG. 19, andthus the same description is not repeated here.

(Step S402)

The arithmetic decoder 402 performs arithmetic decoding on the parameterindicating the decoding-target coefficient using probability informationabout the context selected by the context selecting unit 401.

As described above, the image decoding apparatus 400 configured as shownin FIG. 20 can select a context from the context set corresponding tothe sum of the values indicating the horizontal direction position andthe vertical direction position of the sub-block in the decoding-targetblock. Accordingly, the image decoding apparatus 400 can suppressdecrease in the decoding efficiency and reduce the load for contextselection.

It is to be noted that in each of the embodiments and the variationthereof, each of the structural elements in each of the above-describedembodiments may be configured in the form of an exclusive hardwareproduct, or may be realized by executing a software program suitable forthe structural element. Each of the structural elements may be realizedby means of a program executing unit, such as a CPU and a processor,reading and executing the software program recorded on a recordingmedium such as a hard disk or a semiconductor memory. Here, the softwareprogram for realizing any one of the image coding apparatus and theimage decoding apparatus according to each of the embodiments andvariations thereof etc. is a program described below.

The program is, for example, a program causing a computer to execute animage coding method for coding an image on a block-by-block basis andincluding: selecting, for each of a plurality of sub-blocks included ina coding-target block and each including a plurality of coefficients, acontext for performing arithmetic coding on a parameter indicating acoding-target coefficient included in the sub-block from a context setcorresponding to the sub-block, based on at least one referencecoefficient located around the coding-target coefficient, thecoding-target block being a transform unit; and performing arithmeticcoding on the parameter indicating the coding-target coefficient usingprobability information about the selected context, wherein, in theselecting, the context is selected from the context set, the context setcorresponding to a sum of (i) a value indicating a position in ahorizontal direction of the sub-block in the coding-target block and(ii) a value indicating a position in a vertical direction of thesub-block in the coding-target block.

Alternatively, the program is a program for causing a computer toexecute an image decoding method according to an aspect of the presentdisclosure is an image decoding method for decoding an image coded on ablock-by-block basis and including: selecting, for each of a pluralityof sub-blocks included in a decoding-target block and each including aplurality of coefficients, a context for performing arithmetic decodingon a parameter indicating a decoding-target coefficient included in thesub-block from a context set corresponding to the sub-block, based on atleast one reference coefficient located around the decoding-targetcoefficient, the decoding-target block being a transform unit; andperforming arithmetic decoding on the parameter indicating thedecoding-target coefficient using probability information about theselected context, wherein, in the selecting, the context is selectedfrom the context set, the context set corresponding to a sum of (i) avalue indicating a position in a horizontal direction of the sub-blockin the decoding-target block and (ii) a value indicating a position in avertical direction of the sub-block in the decoding-target block.

Embodiment 3

The processing described in each of embodiments can be simplyimplemented in an independent computer system, by recording, in arecording medium, a program for implementing the configurations of themoving picture coding method (image coding method) and the movingpicture decoding method (image decoding method) described in each ofembodiments. The recording media may be any recording media as long asthe program can be recorded, such as a magnetic disk, an optical disk, amagnetic optical disk, an IC card, and a semiconductor memory.

Hereinafter, the applications to the moving picture coding method (imagecoding method) and the moving picture decoding method (image decodingmethod) described in each of embodiments and systems using thereof willbe described. The system has a feature of having an image coding anddecoding apparatus that includes an image coding apparatus using theimage coding method and an image decoding apparatus using the imagedecoding method. Other configurations in the system can be changed asappropriate depending on the cases.

FIG. 22 illustrates an overall configuration of a content providingsystem ex100 for implementing content distribution services. The areafor providing communication services is divided into cells of desiredsize, and base stations ex106, ex107, ex108, ex109, and ex110 which arefixed wireless stations are placed in each of the cells.

The content providing system ex100 is connected to devices, such as acomputer ex111, a personal digital assistant (PDA) ex112, a cameraex113, a cellular phone ex114 and a game machine ex115, via the Internetex101, an Internet service provider ex102, a telephone network ex104, aswell as the base stations ex106 to ex110, respectively.

However, the configuration of the content providing system ex100 is notlimited to the configuration shown in FIG. 22, and a combination inwhich any of the elements are connected is acceptable. In addition, eachdevice may be directly connected to the telephone network ex104, ratherthan via the base stations ex106 to ex110 which are the fixed wirelessstations. Furthermore, the devices may be interconnected to each othervia a short distance wireless communication and others.

The camera ex113, such as a digital video camera, is capable ofcapturing video. A camera ex116, such as a digital camera, is capable ofcapturing both still images and video. Furthermore, the cellular phoneex114 may be the one that meets any of the standards such as GlobalSystem for Mobile Communications (GSM) (registered trademark), CodeDivision Multiple Access (CDMA), Wideband-Code Division Multiple Access(W-CDMA), Long Term Evolution (LTE), and High Speed Packet Access(HSPA). Alternatively, the cellular phone ex114 may be a PersonalHandyphone System (PHS).

In the content providing system ex100, a streaming server ex103 isconnected to the camera ex113 and others via the telephone network ex104and the base station ex109, which enables distribution of images of alive show and others. In such a distribution, a content (for example,video of a music live show) captured by the user using the camera ex113is coded as described above in each of embodiments (i.e., the camerafunctions as the image coding apparatus according to an aspect of thepresent disclosure), and the coded content is transmitted to thestreaming server ex103. On the other hand, the streaming server ex103carries out stream distribution of the transmitted content data to theclients upon their requests. The clients include the computer ex111, thePDA ex112, the camera ex113, the cellular phone ex114, and the gamemachine ex115 that are capable of decoding the above-mentioned codeddata. Each of the devices that have received the distributed datadecodes and reproduces the coded data (i.e., functions as the imagedecoding apparatus according to an aspect of the present disclosure).

The captured data may be coded by the camera ex113 or the streamingserver ex103 that transmits the data, or the coding processes may beshared between the camera ex113 and the streaming server ex103.Similarly, the distributed data may be decoded by the clients or thestreaming server ex103, or the decoding processes may be shared betweenthe clients and the streaming server ex103. Furthermore, the data of thestill images and video captured by not only the camera ex113 but alsothe camera ex116 may be transmitted to the streaming server ex103through the computer ex111. The coding processes may be performed by thecamera ex116, the computer ex111, or the streaming server ex103, orshared among them.

Furthermore, the coding and decoding processes may be performed by anLSI ex500 generally included in each of the computer ex111 and thedevices. The LSI ex500 may be configured of a single chip or a pluralityof chips. Software for coding and decoding video may be integrated intosome type of a recording medium (such as a CD-ROM, a flexible disk, anda hard disk) that is readable by the computer ex111 and others, and thecoding and decoding processes may be performed using the software.Furthermore, when the cellular phone ex114 is equipped with a camera,the video data obtained by the camera may be transmitted. The video datais data coded by the LSI ex500 included in the cellular phone ex114.

Furthermore, the streaming server ex103 may be composed of servers andcomputers, and may decentralize data and process the decentralized data,record, or distribute data.

As described above, the clients may receive and reproduce the coded datain the content providing system ex100. In other words, the clients canreceive and decode information transmitted by the user, and reproducethe decoded data in real time in the content providing system ex100, sothat the user who does not have any particular right and equipment canimplement personal broadcasting.

Aside from the example of the content providing system ex100, at leastone of the moving picture coding apparatus (image coding apparatus) andthe moving picture decoding apparatus (image decoding apparatus)described in each of embodiments may be implemented in a digitalbroadcasting system ex200 illustrated in FIG. 23. More specifically, abroadcast station ex201 communicates or transmits, via radio waves to abroadcast satellite ex202, multiplexed data obtained by multiplexingaudio data and others onto video data. The video data is data coded bythe moving picture coding method described in each of embodiments (i.e.,data coded by the image coding apparatus according to an aspect of thepresent disclosure). Upon receipt of the multiplexed data, the broadcastsatellite ex202 transmits radio waves for broadcasting. Then, a home-useantenna ex204 with a satellite broadcast reception function receives theradio waves. Next, a device such as a television (receiver) ex300 and aset top box (STB) ex217 decodes the received multiplexed data, andreproduces the decoded data (i.e., functions as the image decodingapparatus according to an aspect of the present disclosure).

Furthermore, a reader/recorder ex218 (i) reads and decodes themultiplexed data recorded on a recording medium ex215, such as a DVD anda BD, or (i) codes video signals in the recording medium ex215, and insome cases, writes data obtained by multiplexing an audio signal on thecoded data. The reader/recorder ex218 can include the moving picturedecoding apparatus or the moving picture coding apparatus as shown ineach of embodiments. In this case, the reproduced video signals aredisplayed on the monitor ex219, and can be reproduced by another deviceor system using the recording medium ex215 on which the multiplexed datais recorded. It is also possible to implement the moving picturedecoding apparatus in the set top box ex217 connected to the cable ex203for a cable television or to the antenna ex204 for satellite and/orterrestrial broadcasting, so as to display the video signals on themonitor ex219 of the television ex300. The moving picture decodingapparatus may be implemented not in the set top box but in thetelevision ex300.

FIG. 24 illustrates the television (receiver) ex300 that uses the movingpicture coding method and the moving picture decoding method describedin each of embodiments. The television ex300 includes: a tuner ex301that obtains or provides multiplexed data obtained by multiplexing audiodata onto video data, through the antenna ex204 or the cable ex203, etc.that receives a broadcast; a modulation/demodulation unit ex302 thatdemodulates the received multiplexed data or modulates data intomultiplexed data to be supplied outside; and amultiplexing/demultiplexing unit ex303 that demultiplexes the modulatedmultiplexed data into video data and audio data, or multiplexes videodata and audio data coded by a signal processing unit ex306 into data.

The television ex300 further includes: a signal processing unit ex306including an audio signal processing unit ex304 and a video signalprocessing unit ex305 that decode audio data and video data and codeaudio data and video data, respectively (which function as the imagecoding apparatus and the image decoding apparatus according to theaspects of the present disclosure); and an output unit ex309 including aspeaker ex307 that provides the decoded audio signal, and a display unitex308 that displays the decoded video signal, such as a display.Furthermore, the television ex300 includes an interface unit ex317including an operation input unit ex312 that receives an input of a useroperation. Furthermore, the television ex300 includes a control unitex310 that controls overall each constituent element of the televisionex300, and a power supply circuit unit ex311 that supplies power to eachof the elements. Other than the operation input unit ex312, theinterface unit ex317 may include: a bridge ex313 that is connected to anexternal device, such as the reader/recorder ex218; a slot unit ex314for enabling attachment of the recording medium ex216, such as an SDcard; a driver ex315 to be connected to an external recording medium,such as a hard disk; and a modem ex316 to be connected to a telephonenetwork. Here, the recording medium ex216 can electrically recordinformation using a non-volatile/volatile semiconductor memory elementfor storage. The constituent elements of the television ex300 areconnected to each other through a synchronous bus.

First, the configuration in which the television ex300 decodesmultiplexed data obtained from outside through the antenna ex204 andothers and reproduces the decoded data will be described. In thetelevision ex300, upon a user operation through a remote controllerex220 and others, the multiplexing/demultiplexing unit ex303demultiplexes the multiplexed data demodulated by themodulation/demodulation unit ex302, under control of the control unitex310 including a CPU. Furthermore, the audio signal processing unitex304 decodes the demultiplexed audio data, and the video signalprocessing unit ex305 decodes the demultiplexed video data, using thedecoding method described in each of embodiments, in the televisionex300. The output unit ex309 provides the decoded video signal and audiosignal outside, respectively. When the output unit ex309 provides thevideo signal and the audio signal, the signals may be temporarily storedin buffers ex318 and ex319, and others so that the signals arereproduced in synchronization with each other. Furthermore, thetelevision ex300 may read multiplexed data not through a broadcast andothers but from the recording media ex215 and ex216, such as a magneticdisk, an optical disk, and a SD card. Next, a configuration in which thetelevision ex300 codes an audio signal and a video signal, and transmitsthe data outside or writes the data on a recording medium will bedescribed. In the television ex300, upon a user operation through theremote controller ex220 and others, the audio signal processing unitex304 codes an audio signal, and the video signal processing unit ex305codes a video signal, under control of the control unit ex310 using thecoding method described in each of embodiments. Themultiplexing/demultiplexing unit ex303 multiplexes the coded videosignal and audio signal, and provides the resulting signal outside. Whenthe multiplexing/demultiplexing unit ex303 multiplexes the video signaland the audio signal, the signals may be temporarily stored in thebuffers ex320 and ex321, and others so that the signals are reproducedin synchronization with each other. Here, the buffers ex318, ex319,ex320, and ex321 may be plural as illustrated, or at least one buffermay be shared in the television ex300. Furthermore, data may be storedin a buffer so that the system overflow and underflow may be avoidedbetween the modulation/demodulation unit ex302 and themultiplexing/demultiplexing unit ex303, for example.

Furthermore, the television ex300 may include a configuration forreceiving an AV input from a microphone or a camera other than theconfiguration for obtaining audio and video data from a broadcast or arecording medium, and may code the obtained data. Although thetelevision ex300 can code, multiplex, and provide outside data in thedescription, it may be capable of only receiving, decoding, andproviding outside data but not the coding, multiplexing, and providingoutside data.

Furthermore, when the reader/recorder ex218 reads or writes multiplexeddata from or on a recording medium, one of the television ex300 and thereader/recorder ex218 may decode or code the multiplexed data, and thetelevision ex300 and the reader/recorder ex218 may share the decoding orcoding.

As an example, FIG. 25 illustrates a configuration of an informationreproducing/recording unit ex400 when data is read or written from or onan optical disk. The information reproducing/recording unit ex400includes constituent elements ex401, ex402, ex403, ex404, ex405, ex406,and ex407 to be described hereinafter. The optical head ex401 irradiatesa laser spot in a recording surface of the recording medium ex215 thatis an optical disk to write information, and detects reflected lightfrom the recording surface of the recording medium ex215 to read theinformation. The modulation recording unit ex402 electrically drives asemiconductor laser included in the optical head ex401, and modulatesthe laser light according to recorded data. The reproductiondemodulating unit ex403 amplifies a reproduction signal obtained byelectrically detecting the reflected light from the recording surfaceusing a photo detector included in the optical head ex401, anddemodulates the reproduction signal by separating a signal componentrecorded on the recording medium ex215 to reproduce the necessaryinformation. The buffer ex404 temporarily holds the information to berecorded on the recording medium ex215 and the information reproducedfrom the recording medium ex215. The disk motor ex405 rotates therecording medium ex215. The servo control unit ex406 moves the opticalhead ex401 to a predetermined information track while controlling therotation drive of the disk motor ex405 so as to follow the laser spot.The system control unit ex407 controls overall the informationreproducing/recording unit ex400. The reading and writing processes canbe implemented by the system control unit ex407 using variousinformation stored in the buffer ex404 and generating and adding newinformation as necessary, and by the modulation recording unit ex402,the reproduction demodulating unit ex403, and the servo control unitex406 that record and reproduce information through the optical headex401 while being operated in a coordinated manner. The system controlunit ex407 includes, for example, a microprocessor, and executesprocessing by causing a computer to execute a program for read andwrite.

Although the optical head ex401 irradiates a laser spot in thedescription, it may perform high-density recording using near fieldlight.

FIG. 26 illustrates the recording medium ex215 that is the optical disk.On the recording surface of the recording medium ex215, guide groovesare spirally formed, and an information track ex230 records, in advance,address information indicating an absolute position on the diskaccording to change in a shape of the guide grooves. The addressinformation includes information for determining positions of recordingblocks ex231 that are a unit for recording data. Reproducing theinformation track ex230 and reading the address information in anapparatus that records and reproduces data can lead to determination ofthe positions of the recording blocks. Furthermore, the recording mediumex215 includes a data recording area ex233, an inner circumference areaex232, and an outer circumference area ex234. The data recording areaex233 is an area for use in recording the user data. The innercircumference area ex232 and the outer circumference area ex234 that areinside and outside of the data recording area ex233, respectively arefor specific use except for recording the user data. The informationreproducing/recording unit 400 reads and writes coded audio, coded videodata, or multiplexed data obtained by multiplexing the coded audio andvideo data, from and on the data recording area ex233 of the recordingmedium ex215.

Although an optical disk having a layer, such as a DVD and a BD isdescribed as an example in the description, the optical disk is notlimited to such, and may be an optical disk having a multilayerstructure and capable of being recorded on a part other than thesurface. Furthermore, the optical disk may have a structure formultidimensional recording/reproduction, such as recording ofinformation using light of colors with different wavelengths in the sameportion of the optical disk and for recording information havingdifferent layers from various angles.

Furthermore, a car ex210 having an antenna ex205 can receive data fromthe satellite ex202 and others, and reproduce video on a display devicesuch as a car navigation system ex211 set in the car ex210, in thedigital broadcasting system ex200. Here, a configuration of the carnavigation system ex211 will be a configuration, for example, includinga GPS receiving unit from the configuration illustrated in FIG. 24. Thesame will be true for the configuration of the computer ex111, thecellular phone ex114, and others.

FIG. 27A illustrates the cellular phone ex114 that uses the movingpicture coding method and the moving picture decoding method describedin embodiments. The cellular phone ex114 includes: an antenna ex350 fortransmitting and receiving radio waves through the base station ex110; acamera unit ex365 capable of capturing moving and still images; and adisplay unit ex358 such as a liquid crystal display for displaying thedata such as decoded video captured by the camera unit ex365 or receivedby the antenna ex350. The cellular phone ex114 further includes: a mainbody unit including an operation key unit ex366; an audio output unitex357 such as a speaker for output of audio; an audio input unit ex356such as a microphone for input of audio; a memory unit ex367 for storingcaptured video or still pictures, recorded audio, coded or decoded dataof the received video, the still pictures, e-mails, or others; and aslot unit ex364 that is an interface unit for a recording medium thatstores data in the same manner as the memory unit ex367.

Next, an example of a configuration of the cellular phone ex114 will bedescribed with reference to FIG. 27B. In the cellular phone ex114, amain control unit ex360 designed to control overall each unit of themain body including the display unit ex358 as well as the operation keyunit ex366 is connected mutually, via a synchronous bus ex370, to apower supply circuit unit ex361, an operation input control unit ex362,a video signal processing unit ex355, a camera interface unit ex363, aliquid crystal display (LCD) control unit ex359, amodulation/demodulation unit ex352, a multiplexing/demultiplexing unitex353, an audio signal processing unit ex354, the slot unit ex364, andthe memory unit ex367.

When a call-end key or a power key is turned ON by a user's operation,the power supply circuit unit ex361 supplies the respective units withpower from a battery pack so as to activate the cell phone ex114.

In the cellular phone ex114, the audio signal processing unit ex354converts the audio signals collected by the audio input unit ex356 invoice conversation mode into digital audio signals under the control ofthe main control unit ex360 including a CPU, ROM, and RAM. Then, themodulation/demodulation unit ex352 performs spread spectrum processingon the digital audio signals, and the transmitting and receiving unitex351 performs digital-to-analog conversion and frequency conversion onthe data, so as to transmit the resulting data via the antenna ex350.Also, in the cellular phone ex114, the transmitting and receiving unitex351 amplifies the data received by the antenna ex350 in voiceconversation mode and performs frequency conversion and theanalog-to-digital conversion on the data. Then, themodulation/demodulation unit ex352 performs inverse spread spectrumprocessing on the data, and the audio signal processing unit ex354converts it into analog audio signals, so as to output them via theaudio output unit ex357.

Furthermore, when an e-mail in data communication mode is transmitted,text data of the e-mail inputted by operating the operation key unitex366 and others of the main body is sent out to the main control unitex360 via the operation input control unit ex362. The main control unitex360 causes the modulation/demodulation unit ex352 to perform spreadspectrum processing on the text data, and the transmitting and receivingunit ex351 performs the digital-to-analog conversion and the frequencyconversion on the resulting data to transmit the data to the basestation ex110 via the antenna ex350. When an e-mail is received,processing that is approximately inverse to the processing fortransmitting an e-mail is performed on the received data, and theresulting data is provided to the display unit ex358.

When video, still images, or video and audio in data communication modeis or are transmitted, the video signal processing unit ex355 compressesand codes video signals supplied from the camera unit ex365 using themoving picture coding method shown in each of embodiments (i.e.,functions as the image coding apparatus according to the aspect of thepresent disclosure), and transmits the coded video data to themultiplexing/demultiplexing unit ex353. In contrast, during when thecamera unit ex365 captures video, still images, and others, the audiosignal processing unit ex354 codes audio signals collected by the audioinput unit ex356, and transmits the coded audio data to themultiplexing/demultiplexing unit ex353.

The multiplexing/demultiplexing unit ex353 multiplexes the coded videodata supplied from the video signal processing unit ex355 and the codedaudio data supplied from the audio signal processing unit ex354, using apredetermined method. Then, the modulation/demodulation unit(modulation/demodulation circuit unit) ex352 performs spread spectrumprocessing on the multiplexed data, and the transmitting and receivingunit ex351 performs digital-to-analog conversion and frequencyconversion on the data so as to transmit the resulting data via theantenna ex350.

When receiving data of a video file which is linked to a Web page andothers in data communication mode or when receiving an e-mail with videoand/or audio attached, in order to decode the multiplexed data receivedvia the antenna ex350, the multiplexing/demultiplexing unit ex353demultiplexes the multiplexed data into a video data bit stream and anaudio data bit stream, and supplies the video signal processing unitex355 with the coded video data and the audio signal processing unitex354 with the coded audio data, through the synchronous bus ex370. Thevideo signal processing unit ex355 decodes the video signal using amoving picture decoding method corresponding to the moving picturecoding method shown in each of embodiments (i.e., functions as the imagedecoding apparatus according to the aspect of the present disclosure),and then the display unit ex358 displays, for instance, the video andstill images included in the video file linked to the Web page via theLCD control unit ex359. Furthermore, the audio signal processing unitex354 decodes the audio signal, and the audio output unit ex357 providesthe audio.

Furthermore, similarly to the television ex300, a terminal such as thecellular phone ex114 probably have 3 types of implementationconfigurations including not only (i) a transmitting and receivingterminal including both a coding apparatus and a decoding apparatus, butalso (ii) a transmitting terminal including only a coding apparatus and(iii) a receiving terminal including only a decoding apparatus. Althoughthe digital broadcasting system ex200 receives and transmits themultiplexed data obtained by multiplexing audio data onto video data inthe description, the multiplexed data may be data obtained bymultiplexing not audio data but character data related to video ontovideo data, and may be not multiplexed data but video data itself.

As such, the moving picture coding method and the moving picturedecoding method in each of embodiments can be used in any of the devicesand systems described. Thus, the advantages described in each ofembodiments can be obtained.

Furthermore, the present invention is not limited to the above-describedembodiments of the present disclosure, and various modifications andrevisions can be made without deviating from the scope of the presentdisclosure.

Embodiment 4

Video data can be generated by switching, as necessary, between (i) themoving picture coding method or the moving picture coding apparatusshown in each of embodiments and (ii) a moving picture coding method ora moving picture coding apparatus in conformity with a differentstandard, such as MPEG-2, MPEG-4 AVC, and VC-1.

Here, when a plurality of video data that conforms to the differentstandards is generated and is then decoded, the decoding methods need tobe selected to conform to the different standards. However, since towhich standard each of the plurality of the video data to be decodedconform cannot be detected, there is a problem that an appropriatedecoding method cannot be selected.

In order to solve the problem, multiplexed data obtained by multiplexingaudio data and others onto video data has a structure includingidentification information indicating to which standard the video dataconforms. The specific structure of the multiplexed data including thevideo data generated in the moving picture coding method and by themoving picture coding apparatus shown in each of embodiments will behereinafter described. The multiplexed data is a digital stream in theMPEG-2 Transport Stream format.

FIG. 28 illustrates a structure of the multiplexed data. As illustratedin FIG. 28, the multiplexed data can be obtained by multiplexing atleast one of a video stream, an audio stream, a presentation graphicsstream (PG), and an interactive graphics stream. The video streamrepresents primary video and secondary video of a movie, the audiostream (IG) represents a primary audio part and a secondary audio partto be mixed with the primary audio part, and the presentation graphicsstream represents subtitles of the movie. Here, the primary video isnormal video to be displayed on a screen, and the secondary video isvideo to be displayed on a smaller window in the primary video.Furthermore, the interactive graphics stream represents an interactivescreen to be generated by arranging the GUI components on a screen. Thevideo stream is coded in the moving picture coding method or by themoving picture coding apparatus shown in each of embodiments, or in amoving picture coding method or by a moving picture coding apparatus inconformity with a conventional standard, such as MPEG-2, MPEG-4 AVC, andVC-1. The audio stream is coded in accordance with a standard, such asDolby-AC-3, Dolby Digital Plus, MLP, DTS, DTS-HD, and linear PCM.

Each stream included in the multiplexed data is identified by PID. Forexample, 0x1011 is allocated to the video stream to be used for video ofa movie, 0x1100 to 0x111F are allocated to the audio streams, 0x1200 to0x121F are allocated to the presentation graphics streams, 0x1400 to0x141F are allocated to the interactive graphics streams, 0x1B00 to0x1B1F are allocated to the video streams to be used for secondary videoof the movie, and 0x1A00 to 0x1A1F are allocated to the audio streams tobe used for the secondary audio to be mixed with the primary audio.

FIG. 29 schematically illustrates how data is multiplexed. First, avideo stream ex235 composed of video frames and an audio stream ex238composed of audio frames are transformed into a stream of PES packetsex236 and a stream of PES packets ex239, and further into TS packetsex237 and TS packets ex240, respectively. Similarly, data of apresentation graphics stream ex241 and data of an interactive graphicsstream ex244 are transformed into a stream of PES packets ex242 and astream of PES packets ex245, and further into TS packets ex243 and TSpackets ex246, respectively. These TS packets are multiplexed into astream to obtain multiplexed data ex247.

FIG. 30 illustrates how a video stream is stored in a stream of PESpackets in more detail. The first bar in FIG. 30 shows a video framestream in a video stream. The second bar shows the stream of PESpackets. As indicated by arrows denoted as yy1, yy2, yy3, and yy4 inFIG. 30, the video stream is divided into pictures as I pictures, Bpictures, and P pictures each of which is a video presentation unit, andthe pictures are stored in a payload of each of the PES packets. Each ofthe PES packets has a PES header, and the PES header stores aPresentation Time-Stamp (PTS) indicating a display time of the picture,and a Decoding Time-Stamp (DTS) indicating a decoding time of thepicture.

FIG. 31 illustrates a format of TS packets to be finally written on themultiplexed data. Each of the TS packets is a 188-byte fixed lengthpacket including a 4-byte TS header having information, such as a PIDfor identifying a stream and a 184-byte TS payload for storing data. ThePES packets are divided, and stored in the TS payloads, respectively.When a BD ROM is used, each of the TS packets is given a 4-byteTP_Extra_Header, thus resulting in 192-byte source packets. The sourcepackets are written on the multiplexed data. The TP_Extra_Header storesinformation such as an Arrival_Time_Stamp (ATS). The ATS shows atransfer start time at which each of the TS packets is to be transferredto a PID filter. The source packets are arranged in the multiplexed dataas shown at the bottom of FIG. 31. The numbers incrementing from thehead of the multiplexed data are called source packet numbers (SPNs).

Each of the TS packets included in the multiplexed data includes notonly streams of audio, video, subtitles and others, but also a ProgramAssociation Table (PAT), a Program Map Table (PMT), and a Program ClockReference (PCR). The PAT shows what a PID in a PMT used in themultiplexed data indicates, and a PID of the PAT itself is registered aszero. The PMT stores PIDs of the streams of video, audio, subtitles andothers included in the multiplexed data, and attribute information ofthe streams corresponding to the PIDs. The PMT also has variousdescriptors relating to the multiplexed data. The descriptors haveinformation such as copy control information showing whether copying ofthe multiplexed data is permitted or not. The PCR stores STC timeinformation corresponding to an ATS showing when the PCR packet istransferred to a decoder, in order to achieve synchronization between anArrival Time Clock (ATC) that is a time axis of ATSs, and an System TimeClock (STC) that is a time axis of PTSs and DTSs.

FIG. 32 illustrates the data structure of the PMT in detail. A PMTheader is disposed at the top of the PMT. The PMT header describes thelength of data included in the PMT and others. A plurality ofdescriptors relating to the multiplexed data is disposed after the PMTheader. Information such as the copy control information is described inthe descriptors. After the descriptors, a plurality of pieces of streaminformation relating to the streams included in the multiplexed data isdisposed. Each piece of stream information includes stream descriptorseach describing information, such as a stream type for identifying acompression codec of a stream, a stream PID, and stream attributeinformation (such as a frame rate or an aspect ratio). The streamdescriptors are equal in number to the number of streams in themultiplexed data.

When the multiplexed data is recorded on a recording medium and others,it is recorded together with multiplexed data information files.

Each of the multiplexed data information files is management informationof the multiplexed data as shown in FIG. 33. The multiplexed datainformation files are in one to one correspondence with the multiplexeddata, and each of the files includes multiplexed data information,stream attribute information, and an entry map.

As illustrated in FIG. 33, the multiplexed data information includes asystem rate, a reproduction start time, and a reproduction end time. Thesystem rate indicates the maximum transfer rate at which a system targetdecoder to be described later transfers the multiplexed data to a PIDfilter. The intervals of the ATSs included in the multiplexed data areset to not higher than a system rate. The reproduction start timeindicates a PTS in a video frame at the head of the multiplexed data. Aninterval of one frame is added to a PTS in a video frame at the end ofthe multiplexed data, and the PTS is set to the reproduction end time.

As shown in FIG. 34, a piece of attribute information is registered inthe stream attribute information, for each PID of each stream includedin the multiplexed data. Each piece of attribute information hasdifferent information depending on whether the corresponding stream is avideo stream, an audio stream, a presentation graphics stream, or aninteractive graphics stream. Each piece of video stream attributeinformation carries information including what kind of compression codecis used for compressing the video stream, and the resolution, aspectratio and frame rate of the pieces of picture data that is included inthe video stream. Each piece of audio stream attribute informationcarries information including what kind of compression codec is used forcompressing the audio stream, how many channels are included in theaudio stream, which language the audio stream supports, and how high thesampling frequency is. The video stream attribute information and theaudio stream attribute information are used for initialization of adecoder before the player plays back the information.

In the present embodiment, the multiplexed data to be used is of astream type included in the PMT. Furthermore, when the multiplexed datais recorded on a recording medium, the video stream attributeinformation included in the multiplexed data information is used. Morespecifically, the moving picture coding method or the moving picturecoding apparatus described in each of embodiments includes a step or aunit for allocating unique information indicating video data generatedby the moving picture coding method or the moving picture codingapparatus in each of embodiments, to the stream type included in the PMTor the video stream attribute information. With the configuration, thevideo data generated by the moving picture coding method or the movingpicture coding apparatus described in each of embodiments can bedistinguished from video data that conforms to another standard.

Furthermore, FIG. 35 illustrates steps of the moving picture decodingmethod according to the present embodiment. In Step exS100, the streamtype included in the PMT or the video stream attribute informationincluded in the multiplexed data information is obtained from themultiplexed data. Next, in Step exS101, it is determined whether or notthe stream type or the video stream attribute information indicates thatthe multiplexed data is generated by the moving picture coding method orthe moving picture coding apparatus in each of embodiments. When it isdetermined that the stream type or the video stream attributeinformation indicates that the multiplexed data is generated by themoving picture coding method or the moving picture coding apparatus ineach of embodiments, in Step exS102, decoding is performed by the movingpicture decoding method in each of embodiments. Furthermore, when thestream type or the video stream attribute information indicatesconformance to the conventional standards, such as MPEG-2, MPEG-4 AVC,and VC-1, in Step exS103, decoding is performed by a moving picturedecoding method in conformity with the conventional standards.

As such, allocating a new unique value to the stream type or the videostream attribute information enables determination whether or not themoving picture decoding method or the moving picture decoding apparatusthat is described in each of embodiments can perform decoding. Even whenmultiplexed data that conforms to a different standard is input, anappropriate decoding method or apparatus can be selected. Thus, itbecomes possible to decode information without any error. Furthermore,the moving picture coding method or apparatus, or the moving picturedecoding method or apparatus in the present embodiment can be used inthe devices and systems described above.

Embodiment 5

Each of the moving picture coding method, the moving picture codingapparatus, the moving picture decoding method, and the moving picturedecoding apparatus in each of embodiments is typically achieved in theform of an integrated circuit or a Large Scale Integrated (LSI) circuit.As an example of the LSI, FIG. 36 illustrates a configuration of the LSIex500 that is made into one chip. The LSI ex500 includes elements ex501,ex502, ex503, ex504, ex505, ex506, ex507, ex508, and ex509 to bedescribed below, and the elements are connected to each other through abus ex510. The power supply circuit unit ex505 is activated by supplyingeach of the elements with power when the power supply circuit unit ex505is turned on.

For example, when coding is performed, the LSI ex500 receives an AVsignal from a microphone ex117, a camera ex113, and others through an AVIO ex509 under control of a control unit ex501 including a CPU ex502, amemory controller ex503, a stream controller ex504, and a drivingfrequency control unit ex512. The received AV signal is temporarilystored in an external memory ex511, such as an SDRAM. Under control ofthe control unit ex501, the stored data is segmented into data portionsaccording to the processing amount and speed to be transmitted to asignal processing unit ex507. Then, the signal processing unit ex507codes an audio signal and/or a video signal. Here, the coding of thevideo signal is the coding described in each of embodiments.Furthermore, the signal processing unit ex507 sometimes multiplexes thecoded audio data and the coded video data, and a stream IO ex506provides the multiplexed data outside. The provided multiplexed data istransmitted to the base station ex107, or written on the recordingmedium ex215. When data sets are multiplexed, the data should betemporarily stored in the buffer ex508 so that the data sets aresynchronized with each other.

Although the memory ex511 is an element outside the LSI ex500, it may beincluded in the LSI ex500. The buffer ex508 is not limited to onebuffer, but may be composed of buffers. Furthermore, the LSI ex500 maybe made into one chip or a plurality of chips.

Furthermore, although the control unit ex501 includes the CPU ex502, thememory controller ex503, the stream controller ex504, the drivingfrequency control unit ex512, the configuration of the control unitex501 is not limited to such. For example, the signal processing unitex507 may further include a CPU. Inclusion of another CPU in the signalprocessing unit ex507 can improve the processing speed. Furthermore, asanother example, the CPU ex502 may serve as or be a part of the signalprocessing unit ex507, and, for example, may include an audio signalprocessing unit. In such a case, the control unit ex501 includes thesignal processing unit ex507 or the CPU ex502 including a part of thesignal processing unit ex507.

The name used here is LSI, but it may also be called IC, system LSI,super LSI, or ultra LSI depending on the degree of integration.

Moreover, ways to achieve integration are not limited to the LSI, and aspecial circuit or a general purpose processor and so forth can alsoachieve the integration. Field Programmable Gate Array (FPGA) that canbe programmed after manufacturing LSIs or a reconfigurable processorthat allows re-configuration of the connection or configuration of anLSI can be used for the same purpose.

In the future, with advancement in semiconductor technology, a brand-newtechnology may replace LSI. The functional blocks can be integratedusing such a technology. The possibility is that the present disclosureis applied to biotechnology.

Embodiment 6

When video data generated in the moving picture coding method or by themoving picture coding apparatus described in each of embodiments isdecoded, compared to when video data that conforms to a conventionalstandard, such as MPEG-2, MPEG-4 AVC, and VC-1 is decoded, theprocessing amount probably increases. Thus, the LSI ex500 needs to beset to a driving frequency higher than that of the CPU ex502 to be usedwhen video data in conformity with the conventional standard is decoded.However, when the driving frequency is set higher, there is a problemthat the power consumption increases.

In order to solve the problem, the moving picture decoding apparatus,such as the television ex300 and the LSI ex500 is configured todetermine to which standard the video data conforms, and switch betweenthe driving frequencies according to the determined standard. FIG. 37illustrates a configuration ex800 in the present embodiment. A drivingfrequency switching unit ex803 sets a driving frequency to a higherdriving frequency when video data is generated by the moving picturecoding method or the moving picture coding apparatus described in eachof embodiments. Then, the driving frequency switching unit ex803instructs a decoding processing unit ex801 that executes the movingpicture decoding method described in each of embodiments to decode thevideo data. When the video data conforms to the conventional standard,the driving frequency switching unit ex803 sets a driving frequency to alower driving frequency than that of the video data generated by themoving picture coding method or the moving picture coding apparatusdescribed in each of embodiments. Then, the driving frequency switchingunit ex803 instructs the decoding processing unit ex802 that conforms tothe conventional standard to decode the video data.

More specifically, the driving frequency switching unit ex803 includesthe CPU ex502 and the driving frequency control unit ex512 in FIG. 36.Here, each of the decoding processing unit ex801 that executes themoving picture decoding method described in each of embodiments and thedecoding processing unit ex802 that conforms to the conventionalstandard corresponds to the signal processing unit ex507 in FIG. 36. TheCPU ex502 determines to which standard the video data conforms. Then,the driving frequency control unit ex512 determines a driving frequencybased on a signal from the CPU ex502. Furthermore, the signal processingunit ex507 decodes the video data based on the signal from the CPUex502. For example, the identification information described inEmbodiment 4 is probably used for identifying the video data. Theidentification information is not limited to the one described inEmbodiment 4 but may be any information as long as the informationindicates to which standard the video data conforms. For example, whenwhich standard video data conforms to can be determined based on anexternal signal for determining that the video data is used for atelevision or a disk, etc., the determination may be made based on suchan external signal. Furthermore, the CPU ex502 selects a drivingfrequency based on, for example, a look-up table in which the standardsof the video data are associated with the driving frequencies as shownin FIG. 39. The driving frequency can be selected by storing the look-uptable in the buffer ex508 and in an internal memory of an LSI, and withreference to the look-up table by the CPU ex502.

FIG. 38 illustrates steps for executing a method in the presentembodiment. First, in Step exS200, the signal processing unit ex507obtains identification information from the multiplexed data. Next, inStep exS201, the CPU ex502 determines whether or not the video data isgenerated by the coding method and the coding apparatus described ineach of embodiments, based on the identification information. When thevideo data is generated by the moving picture coding method and themoving picture coding apparatus described in each of embodiments, inStep exS202, the CPU ex502 transmits a signal for setting the drivingfrequency to a higher driving frequency to the driving frequency controlunit ex512. Then, the driving frequency control unit ex512 sets thedriving frequency to the higher driving frequency. On the other hand,when the identification information indicates that the video dataconforms to the conventional standard, such as MPEG-2, MPEG-4 AVC, andVC-1, in Step exS203, the CPU ex502 transmits a signal for setting thedriving frequency to a lower driving frequency to the driving frequencycontrol unit ex512. Then, the driving frequency control unit ex512 setsthe driving frequency to the lower driving frequency than that in thecase where the video data is generated by the moving picture codingmethod and the moving picture coding apparatus described in each ofembodiment.

Furthermore, along with the switching of the driving frequencies, thepower conservation effect can be improved by changing the voltage to beapplied to the LSI ex500 or an apparatus including the LSI ex500. Forexample, when the driving frequency is set lower, the voltage to beapplied to the LSI ex500 or the apparatus including the LSI ex500 isprobably set to a voltage lower than that in the case where the drivingfrequency is set higher.

Furthermore, when the processing amount for decoding is larger, thedriving frequency may be set higher, and when the processing amount fordecoding is smaller, the driving frequency may be set lower as themethod for setting the driving frequency. Thus, the setting method isnot limited to the ones described above. For example, when theprocessing amount for decoding video data in conformity with MPEG-4 AVCis larger than the processing amount for decoding video data generatedby the moving picture coding method and the moving picture codingapparatus described in each of embodiments, the driving frequency isprobably set in reverse order to the setting described above.

Furthermore, the method for setting the driving frequency is not limitedto the method for setting the driving frequency lower. For example, whenthe identification information indicates that the video data isgenerated by the moving picture coding method and the moving picturecoding apparatus described in each of embodiments, the voltage to beapplied to the LSI ex500 or the apparatus including the LSI ex500 isprobably set higher. When the identification information indicates thatthe video data conforms to the conventional standard, such as MPEG-2,MPEG-4 AVC, and VC-1, the voltage to be applied to the LSI ex500 or theapparatus including the LSI ex500 is probably set lower. As anotherexample, when the identification information indicates that the videodata is generated by the moving picture coding method and the movingpicture coding apparatus described in each of embodiments, the drivingof the CPU ex502 does not probably have to be suspended. When theidentification information indicates that the video data conforms to theconventional standard, such as MPEG-2, MPEG-4 AVC, and VC-1, the drivingof the CPU ex502 is probably suspended at a given time because the CPUex502 has extra processing capacity. Even when the identificationinformation indicates that the video data is generated by the movingpicture coding method and the moving picture coding apparatus describedin each of embodiments, in the case where the CPU ex502 has extraprocessing capacity, the driving of the CPU ex502 is probably suspendedat a given time. In such a case, the suspending time is probably setshorter than that in the case where when the identification informationindicates that the video data conforms to the conventional standard,such as MPEG-2, MPEG-4 AVC, and VC-1.

Accordingly, the power conservation effect can be improved by switchingbetween the driving frequencies in accordance with the standard to whichthe video data conforms. Furthermore, when the LSI ex500 or theapparatus including the LSI ex500 is driven using a battery, the batterylife can be extended with the power conservation effect.

Embodiment 7

There are cases where a plurality of video data that conforms todifferent standards, is provided to the devices and systems, such as atelevision and a cellular phone. In order to enable decoding theplurality of video data that conforms to the different standards, thesignal processing unit ex507 of the LSI ex500 needs to conform to thedifferent standards. However, the problems of increase in the scale ofthe circuit of the LSI ex500 and increase in the cost arise with theindividual use of the signal processing units ex507 that conform to therespective standards.

In order to solve the problem, what is conceived is a configuration inwhich the decoding processing unit for implementing the moving picturedecoding method described in each of embodiments and the decodingprocessing unit that conforms to the conventional standard, such asMPEG-2, MPEG-4 AVC, and VC-1 are partly shared. Ex900 in FIG. 40A showsan example of the configuration. For example, the moving picturedecoding method described in each of embodiments and the moving picturedecoding method that conforms to MPEG-4 AVC have, partly in common, thedetails of processing, such as entropy coding, inverse quantization,deblocking filtering, and motion compensated prediction. The details ofprocessing to be shared probably include use of a decoding processingunit ex902 that conforms to MPEG-4 AVC. In contrast, a dedicateddecoding processing unit ex901 is probably used for other processingunique to an aspect of the present disclosure. Since the aspect of thepresent disclosure is characterized by entropy decoding in particular,for example, the dedicated decoding processing unit ex901 is used forentropy decoding. Otherwise, the decoding processing unit is probablyshared for one of the inverse quantization, deblocking filtering, andmotion compensation, or all of the processing. The decoding processingunit for implementing the moving picture decoding method described ineach of embodiments may be shared for the processing to be shared, and adedicated decoding processing unit may be used for processing unique tothat of MPEG-4 AVC.

Furthermore, ex1000 in FIG. 40B shows another example in that processingis partly shared. This example uses a configuration including adedicated decoding processing unit ex1001 that supports the processingunique to an aspect of the present disclosure, a dedicated decodingprocessing unit ex1002 that supports the processing unique to anotherconventional standard, and a decoding processing unit ex1003 thatsupports processing to be shared between the moving picture decodingmethod according to the aspect of the present disclosure and theconventional moving picture decoding method. Here, the dedicateddecoding processing units ex1001 and ex1002 are not necessarilyspecialized for the processing according to the aspect of the presentdisclosure and the processing of the conventional standard,respectively, and may be the ones capable of implementing generalprocessing. Furthermore, the configuration of the present embodiment canbe implemented by the LSI ex500.

As such, reducing the scale of the circuit of an LSI and reducing thecost are possible by sharing the decoding processing unit for theprocessing to be shared between the moving picture decoding methodaccording to the aspect of the present disclosure and the moving picturedecoding method in conformity with the conventional standard.

1-18. (canceled)
 19. An image decoding method for decoding an imagecoded on a block-by-block basis, the image decoding method comprising:selecting, for each of a plurality of sub-blocks included in adecoding-target block and each including a plurality of coefficients, acontext for performing arithmetic decoding on a parameter indicating adecoding-target coefficient included in the sub-block from a context setcorresponding to the sub-block, based on at least one referencecoefficient located around the decoding-target coefficient, thedecoding-target block being a transform unit; and performing arithmeticdecoding on the parameter indicating the decoding-target coefficientusing probability information about the selected context, wherein, inthe selecting, the context is selected from the context set, the contextset corresponding to a sum of (i) a horizontal value indicating aposition in a horizontal direction of the sub-block in thedecoding-target block and (ii) a vertical value indicating a position ina vertical direction of the sub-block in the decoding-target block, thehorizontal value is an integer part of (a horizontal position of thecoding-target coefficient/4), where the horizontal position of thecoding target coefficient is a horizontal direction distance from aposition of an upper left coefficient in the coding-target block, thevertical value is an integer part of (a vertical position of thecoding-target coefficient/4), where the vertical position of the codingtarget coefficient is a vertical direction distance from the position ofthe upper left coefficient in the coding-target block, and in theselecting, (i) when the sum is smaller than or equal to a thresholdvalue, the context is selected from a first context set and (ii) whenthe sum is larger than the threshold value, the context is selected froma second context set different from the first context set.
 20. The imagedecoding method according to claim 19, wherein, in the selecting, thethreshold value increases with an increase in the size of thedecoding-target block.
 21. The image decoding method according to claim19, wherein the at least one reference coefficient is a coefficient of afrequency component higher than a frequency component having thedecoding-target coefficient.
 22. The image decoding method according toclaim 19, wherein the parameter indicating the decoding-targetcoefficient is a flag indicating whether the decoding-target coefficientis 0 or not.
 23. The image decoding method according to claim 19,wherein the at least one reference coefficient is a plurality ofreference coefficients, and the context selected in the selectingcorresponds to a total number of reference coefficients having anon-zero value among the plurality of reference coefficients.
 24. Theimage decoding method according to claim 19, further comprising: makinga switch between a first decoding process conforming to a first standardand a second decoding process conforming to a second standard, accordingto identification information indicating one of the first standard andthe second standard and added to a bitstream; when the switch is made tothe first decoding process, the selecting and the arithmetic decodingare performed as the first decoding process.
 25. An image decodingapparatus which decodes an image coded on a block-by-block basis, theimage decoding apparatus comprising: a context selecting unit configuredto select, for each of a plurality of sub-blocks included in adecoding-target block and each including a plurality of coefficients, acontext for performing arithmetic decoding on a parameter indicating adecoding-target coefficient included in the sub-block from a context setcorresponding to the sub-block, based on at least one referencecoefficient located around the decoding-target coefficient, thedecoding-target block being a transform unit; and an arithmetic decoderconfigured to perform arithmetic decoding on the parameter indicatingthe decoding-target coefficient using probability information about theselected context, wherein, the context selecting unit is configured toselect the context from the context set, the context set correspondingto a sum of (i) a horizontal value indicating a position in a horizontaldirection of the sub-block in the decoding-target block and (ii) avertical value indicating a position in a vertical direction of thesub-block in the decoding-target block, the horizontal value is aninteger part of (a horizontal position of the coding-targetcoefficient/4), where the horizontal position of the coding targetcoefficient is a horizontal direction distance from a position of anupper left coefficient in the coding-target block, the vertical value isan integer part of (a vertical position of the coding-targetcoefficient/4), where the vertical position of the coding targetcoefficient is a vertical direction distance from the position of theupper left coefficient in the coding-target block, and (i) when the sumis smaller than or equal to a threshold value, the context selectingunit is configured to select the context from a first context set and(ii) when the sum is larger than the threshold value, the contextselecting unit is configured to select the context from a second contextset different from the first context set.
 26. An image decodingapparatus which decodes an image coded on a block-by-block basis, theimage decoding apparatus comprising: a processor; and a non-transitorymemory having stored thereon executable instructions, which whenexecuted, cause the processor to perform: selecting, for each of aplurality of sub-blocks included in a decoding-target block and eachincluding a plurality of coefficients, a context for performingarithmetic decoding on a parameter indicating a decoding-targetcoefficient included in the sub-block from a context set correspondingto the sub-block, based on at least one reference coefficient locatedaround the decoding-target coefficient, the decoding-target block beinga transform unit; and performing arithmetic decoding on the parameterindicating the decoding-target coefficient using probability informationabout the selected context, wherein, in the selecting, the context isselected from the context set, the context set corresponding to a sum of(i) a horizontal value indicating a position in a horizontal directionof the sub-block in the decoding-target block and (ii) a vertical valueindicating a position in a vertical direction of the sub-block in thedecoding-target block, the horizontal value is an integer part of (ahorizontal position of the coding-target coefficient/4), where thehorizontal position of the coding target coefficient is a horizontaldirection distance from a position of an upper left coefficient in thecoding-target block, the vertical value is an integer part of (avertical position of the coding-target coefficient/4), where thevertical position of the coding target coefficient is a verticaldirection distance from the position of the upper left coefficient inthe coding-target block, and in the selecting, (i) when the sum issmaller than or equal to a threshold value, the context is selected froma first context set and (ii) when the sum is larger than the thresholdvalue, the context is selected from a second context set different fromthe first context set.